Insane

Insane is a mental trait in The Sims 3. First available at birth. ''Insane Sims respond to events in life unpredictably. They say what they want, do what they want and even wear what they want. Even if it doesn't make sense to anyone else.''

Attributes

 * When choosing clothes, your Sim picks what feels right, and not necessarily what "is" right.
 * Sim makes decisions on a whim!
 * Sim's wishes may not always make sense.
 * Provides a bonus to Sims writing in the Auto-Biography genre.

Unlocked interactions

 * Fish in swimming pools.
 * Friendly
 * Catch anything?
 * Speak Madness
 * Tell ghost story
 * Talk about conspiracies
 * Sim has the 'Talk to Self' option, which is fulfilling Social and Fun need for him/herself.

Player notes

 * Sim's response to a marriage proposal will be random and not based on relationship level.
 * Insane Sims are not affected by ghosts.
 * Insane Sims can talk to themselves to fill both the social and fun motives, alleviating both the Lonely and Stressed Out moodlet.
 * Insane Sims can create distorted paintings using Paint Stylized Still-Life.
 * Insane Sims will autonomously sit on a toilet or in a bathtub without using it.
 * The Speak Madness social interaction will creep-out non-insane Sims but will entertain other Sims with the Insane trait, and give out a bonus in relationship the first time if the sims has not found each others' Insane Trait (and mark it as discovered). It takes a very high relationship, presumably best friend level, to get a sane sim to react positively to the said interaction.
 * When idle, they will swat flies in the air and eat them, chase their elbows and act like a dog, or choke themselves with their hands.
 * Like Childish Sims, an Insane Sim can gain fishing skill while Fishing in the pool.
 * Insane Sims autonomously consume fruits from the inventory even when not hungry, often yielding the Stuffed moodlet.
 * Insane Sims may exercise and/or go on computers on parties, giving the "Rude Guest" moodlet to the host, unless the Insane Sim in question has the Inappropriate Trait.
 * Insane Sims may get the wish simply to go out at random.
 * With Pets installed, Insane Sims may sometimes act like one of the major pet animals.
 * There is a glitch with the Insane trait, if you have an Insane Child Sim, and pets is installed, the kids may start streching because there was no animation for kids doing the "Acting like a horse".

Examples of insane Sims in The Sims 3
Gus Hart, Dorie Hart, Meadow Carpenter-Rhodes, Hunter Cottoneye, Marigold Racket