There is so much it's hard to narrow down one thing. But something that is like kryptonite for me is hips. When a girl has the right proportion it almost triggers something geneticly/instinctive that absolutely drives me nuts nearly makes me want to get barbaric!!! And if she really knows how to work them hips!! AAAARRRGGGHHHH!!!! (but she has to have dark shiny hair otherwise it doesn't have it's full kryptonic effect)
for the girls out their that think they have big hips, it may be right up some guys alley!!