I vote for Eminem. I hate rap to begin with, but he takes it to an all-time foulness.
When rap started out, it was about having a party, going out to have a good time and the most you worried about was going over your best friend's house to eat and the chicken tastes like wood. Then it made this horrible mutation into "hip/hop/rap" crap where all you hear about is bytches, ho's, drinking, drugging, stealing, pimping, and doing absolutely nothing constructive in society.
Then we had "Wiggah's" come out. Great. Nice. Nothing like bringing this stupid shyt into mainstream.
Okay, getting off my soapbox.