L4D2
Specifically the single shot sniper rifle/assault weapon thing. I'm okay for a little bit, but after I'd say about 5 minutes of hearing the "bang...... bang...... bang" noise of the weapon it starts to give me a really bad headache, so much in fact I've had to turn the game off. It's probably one of only five or six games that I can remember that has make me stop playing due to making me feel ill or giving me a headache after a short period of time. Two others would be Alice, which made me disoritentated, and Hexen will made me feel physically sick.