For me the absolute worst is probably FPS. Although I'm alright with (single-player in) Bioshock but see games such as Left 4 Dead? Jeez, no. That's alright, mind you, because I don't particularly like the game anyway. Far too boring and repetitive for my personal liking.
I would say fighting games; I've been Godawful at them ever since I played Street Fighter Turbo on the SNES back in the day (I used to plug in the other controller so I could actually feel some sense of achievement!) but I don't like fighting games in general in the slightest. Probably because I couldn't play them if my life depended on it but whoopdy-doo, sure. I like my puzzles, point-and-click, adventure RPGs (with the exception of conditional turn based strategies, never liked that with the exception of Pokémon on the Gameboy Color) and platformers. Erk. Well. Kinda.