wow, I was just thinking about doing a thread like this. Okay, mine:
Usher: the epitome of everything I hate
Kanye West: Decent music, quite possibly the most horrendous ego and personality I've ever seen
Madonna: A female version of #1
I'll throw in an honorable ass kicking mention for Gwen Stefani, who suddenly turned from a suburban white chick to a ghetto girl so drastically that it would make Foxy Brown look like Jewel.
That goes for anyone who suddenly develops "blaccent", i.e. Justin Timberlake, Carson Daly whenever he's speaking to a black individual, etc.