sim traits

This page will hold notes that I've discovered about each of the traits that are available in The Sims 3.  Yes, I know this list is far from complete right now; I will add to the list as I verify information and have time to update it.
absent-minded
Sometimes when a sim with this trait enters a room, the current task will be autonomously cancelled as if the sim forgot why she entered the room.
adventurous trait iconadventurous
Sims with the adventurous trait will have a positive "Adventuring" moodlet appear when entering any tomb, giving them an instant +10 mood boost.
Added with: World Adventures.
ambitious trait iconambitious
A sim with this trait is particularly driven to succeed, especially at work. They are happiest when they are moving toward the top level of the career, and get anxious when they seem stalled at any step or worse when they are demoted. They also get higher rewards from fulfilling wishes than other sims.
angler
Angler sims are more adept at the fishing skill than other sims. They learn the skill faster and catch more, bigger and higher quality fish than other sims. These sims will always have fun while they are fishing and can use fishing as stress relief. This trait pairs well with gardener and natural cook traits because fish can be used both as fertilizer and as meal ingredients; and for the Supernatural expansion pack, some fish are also useful as ingredients to alchemists.
animal lover
Added with: Pets.
artistic
athletic trait iconathletic
Athletic sims learn the athletic skill faster than other sims. They like to talk about athletics with other sims, they can work out longer and they aren't fatigued as often or as much as other sims after a work out. With the addition of the University Life expansion pack, this is a good trait for jocks and for sims that pursue the physical education degree.
Opposite of: couch potato
avant garde
Added with: University Life.
bookworm
Sims with this trait love books. They love to read them and they love to be around them. They read books faster than other sims and are more likely to get wishes to read more books.
born salesman/saleswoman
Added with: Ambitions.
brave trait iconbrave
When a sim with the brave trait is inspecting a hole in a wall or in the floor, an arm covered with insects will not bother the sim.  The sim will brush the insects off and continue inspecting the hole.  Brave sims will also recover faster from being caught in a trap and will be able to disarm or try crossing the trap much more quickly.
Opposite of: coward
brooding
can't stand art trait iconcan't stand art
Sims who can't stand art will not appreciate any form of art, from painting to sculpture (but they can get the enjoying music moodlet when they are in rooms with music playing). The best home decorations for sims with this trait are no decorations and very austere surroundings.
cat person
Added with: Pets.
charismatic
Sims with the charismatic trait will have more social interactions available when talking to other sims and their interactions are more likely to have a positive outcome.  Charismatic sims will also build the charisma skill faster than other sims.
Opposite of: socially awkward.
childish
Childish sims are able to interact with objects for younger sims, such as the dollhouse.
clumsy trait iconclumsy
Clumsy sims are much more likely to drop things, like the updated cell phone that was added with the University Life expansion pack; this can shatter the front glass (which appears in the thumbnail image of the phone and on all interactions with the phone interface such as blogging or checking social statuses) and it can only be fixed by buying a new phone.  These sims are also apt to trip and stumble when they are walking, or sometimes even when they are just standing still.
See also: unlucky.
commitment issues
Sims with commitment issues are not happy in long-term relationships.  A sim with this trait who gets married will have negative moodlets related to the feeling of being trapped.
Opposite of: family oriented.
computer whiz
Sims with this trait are very effective when they are using the computer. They can upgrade the computer sooner and with better results. They can hack money into their personal accounts more often successfully and for larger amounts.
Opposite of: technophobe.
daredevil trait icondaredevil
Daredevils love extreme activities and will often try to take everyday activities to the extreme. These sims are well-prepared to fight mummies (in World Adventures) and sharks (in Island Paradise) or to explore the catacombs under the graveyard. This trait also opens up several interactions with other sims where the daredevil sim will perform some feat of bravery.
See also: brave
disciplined
Disciplined sims will build skills, especially the martial arts skill, faster than other sims.
Added with: World Adventures.
dislikes children
Sims who dislike children will not be happy when they are around children, and in some cases even teen sims.  They normally will not initiate any wishes to "have a child with..." any other sim, and they are very much not inclined to care for babies (activities like feeding them or changing diapers).  In short, if you want to build a sim family with lots of kids, a sim who dislikes children is definitely not a good parent candidate.
dramatic trait icondramatic
Sims with this trait will tend to exaggerate emotions to get the response they want from other sims. Dramatic sims will fake passing out for attention.
eccentric trait iconeccentric
An eccentric sim is one who is able to make connections where other sims don't see them. He will create more and higher quality inventions than other sims.
Added with: Ambitions
excitable
Excitable sims have a tendency to become excited over much less than other sims.  Be careful because the sim could easily become excited in a bad way when things do not work out.
evil trait iconevil
Evil sims delight in doing harm and causing mayhem. They are pleased when sims around them are having a bad day. They will have wishes related to doing bad to other sims such as stealing candy from babies. Evil sims are more likely to get into and then win fights, and they excel in the criminal career. Also, evil sims don't mind if rooms are unlit.
family oriented
Sims with this trait will be happiest among family members. They are dedicated to their family members and have more success in long-term relationships.
Opposite of: commitment issues.
friendly trait iconfriendly
A friendly sim is a nice sim. Friendly interactions with other sims are much more likely to be successful, and friendly sims don't mind as often when other sims repeat interactions.
See also: charismatic
frugal trait iconfrugal
Frugal sims love to save money wherever they can. They can clip coupons from the daily newspaper and will often have wishes to buy items with coupons or on sale.
gatherer trait icongatherer
When a sim with this trait picks up a collectible item, there will often be a new want appearing to gather a certain number of them.  For example, after picking up a gem, the sim will often have the desire to "Collect 15 gems" appear.
grumpy
For one of the few traits that shares its name with one of the seven dwarves, this trait's main disadvantage really isn't as much of a disadvantage as you might think at first. Grumpy sims will quickly find themselves in bad moods when things don't go right.
handy trait iconhandy
Handy sims know the difference between a screwdriver and a hammer. They can fix broken objects faster and more often successfully, and they develop the handiness skill faster than other sims. As handiness is one of the skills needed for the military career, this is a good trait to give aspiring astronaut sims.
hopeless romantic trait iconhopeless romantic
Romantic interactions initiated by sims with this trait have a higher probability of success.
loner
Loner sims are happiest when they are alone; when they are in a room with no other sims, they will get the "enjoying solitude" moodlet, which gives them a +15 mood boost.
loves the outdoors trait iconloves the outdoors
Sims that love the outdoors are happiest when they are outside. They often will feel one with nature when they are outdoors. Sims with this trait will also choose to sit outdoors to eat their meals whenever possible.
Opposite of: hates the outdoors
lucky trait iconlucky
Lucky sims have a higher chance of all interactions resulting in positive outcomes. Lucky sims will also rise from bed once in a while with the Feeling Lucky moodlet giving them a more pleasant start to their day.
Opposite of: unlucky
natural cook
Sims with this trait are at home when they are in front of a stove. They make higher quality meals, learn the cooking skill faster, never burn the food they are cooking and they never cause fires from their cooking. This is, obviously, one of the best traits to give to sims who aspire to become celebrity chefs. These sims can even "kick it up a notch" with some extra seasoning after cooking meals. For even better quality meals, have a natural cook learn fishing and gardening so he can get higher quality ingredients for less money, which leads to even higher quality and more satisfying meals.
neat trait iconneat
Sims with this trait will always want to clean things. They will often have wishes related to cleaning their surroundings appear in their list, and they are able to clean things even when they are in a bad mood. These sims will autonomously wash their hands after using the restroom.
Opposite of: slob
neurotic trait iconneurotic
These sims are always a little bit off. They tend to have wants pop up in their list that seem a little obsessive-compulsive, such as a desire to wash hands three times or brush teeth three times. Neurotic sims also once in a while become worried about simple things like the sink or stove; when these worry moodlets appear, have the sim check the item that is worrying them for an instant mood boost.
over emotional
Emotions run a little more freely with these sims. They are more apt to react angrily when bad things happen and also more likely to celebrate when good things happen.
perfectionist
A perfectionist sim will continue working on whatever task he is doing until everything is completely perfect and done. This sim will take longer to perform simple tasks than other sims, but the results will often be of higher quality than that of other sims as well.
sailor trait iconsailor
Natural born sailors love being on boats and the rocking of the boat doesn't seem to bother them like it would other sims. Sailors are also more successful at fishing when they fish from a boat.
Added with: Island Paradise
schmoozer trait iconschmoozer
Schmoozer sims find that they will often be able to get what they want when they are asking other sims for things. These sims' conversations with their bosses and coworkers are more productive and they are more able to flatter and praise other sims.
See also: charismatic and friendly
slob
Sims with the slob trait will not autonomously (most of the time) clean up after themselves.  They will not be as bothered by dirty surroundings as other sims.
Opposite of: neat
unlucky
For some sims, bad things just seem to happen more often to them than to other sims.  Unlucky sims have a higher chance of burning the meals they are cooking, breaking appliances (such as clogging toilets, creating sprays on tubs, showers or sinks, or breaking elctronics like TVs or radios) accidentally starting fires or being visited by thieves.  These sims will also sometimes wake up with an unlucky negative moodlet that lasts the rest of the day.
See also: clumsy.
Opposite of: lucky.
vehicle enthusiast trait iconvehicle enthusiast
Some sims are born gearheads. They love cars and anything that has to do with them. These sims will name their vehicles and will build relationships with their vehicles, very quickly becoming close friends with them.
Added with: Fast Lane Stuff.
virtuoso trait iconvirtuoso
Sims with this trait are naturals with music. They learn how to play musical instruments faster (including the toy xylophone when they are toddlers), and they get more and higher tips when playing music in public. With the addition of the Showtime expansion pack, virtuoso sims can advance through the singer career faster and with less effort than other sims.
workaholic trait iconworkaholic
Sims who love to work will be happiest when they are at work. Workaholic sims will put in the extra effort and earn promotions and raises more quickly than other sims.