Evil. I get tickled that they find so much joy when others around them are miserable. It's like one of those you can't help but laugh at it kind of things. I like the evil laugh also it's so over the top.
I pair it with different things to have a different sort of evil sim frequently. Good or bad traits really.
If I want an outwardly evil guy I make them evil and mean and some other negative trait. If I want a take over the world kind of evil character they might be an evil genius with any other traits that fit. I think the traits vary depending on what I want their personality to be and what type of self control I think they would have.
I find it really hard to deal with a squeamish character trait.. it's hard to get anything done. It's kind of fun to give a sidekick character that trait though especially if I don't play them much.