During create a sim under basics you will be able to change the sims name (first and last), age, skin color, WEIGHT, muscle size, muscle tone, and for female sims, breast size. Hoped this helped! :)
I don't think that they have an actual devious trait, although I remember that in one of the commercial/preview they had for it. I think that that was from the old version before they edited it for...
I saw on a youtube video made by Sims 3 about killing your sims (Don't ask, I get rather bored) and they mentioned making your Sims fat and they can diabetes. However, I have zillions of fat Sims but...