No Sense of Humor, Grumpy, Hot Headed, Perfectionist and Unflirty were the most difficult. Hot Headed Sims seem to always have grudges, while No Sense of Humor Sims are offended and kick Childish Sims and Sims with Sense of humor out. Grumpy sims are always in bad moods no matter what, and Unflirty Sims are harder to get the relationship meter up...I also don't like the Nerotic trait...and the Coward trait is amusing but also dangerous.
however, I like the Evil, Childish and Insane traits the best: I love it when they get options "Do Evil Dance" "Make Evil Drinks" "Evil Drink" "Evil Shower" "Evil Slumber" and that Evil Glow...*in Cartman's voice* Sweet!!!! I love when they go on the computer and have the "Troll on Forum" option that's pretty funny. I'm not an evil person, real life or Sims, I just think the "evil" interactions are sweet. I love the Childish trait, mainly because I'm pretty childish (and I made my sim childish too). NOTE TO CARL: Unlike most sims, childish sims can read "child devolopment" books alone, and will have both options "Read" and "Read With" when a toddler is present. Insane sims are fun too. They sit on toliets, wear bunny slippers to the park, work out in their formal outfits, swim in their pj's, etc. too funny. The sim I made of my cousin is insane and she went to the Bistro in her PJ's haha.