Someones said it before, but bad camera angles are a pain.
Apart from that, it's really bad game glitches I hate, I know some of these are just accidently looked over but when you get a game filled with bugs, it takes the enjoyment out of it.
For example, Tomb Raider: Angel of Darkness.
You'd be sneaking along a wall, the camera angle flips and you're suddenly inside Lara's head, looking at the inside of her eyes and mouth, and let me tell you something, that's scary.
Sometimes you'd be runing along, go for a jump, and the camera angle would flip and you'd miss.
Worst one I can remeber from this game though was when you died. Lara gets shot/falls into a pit/gets spiked/blows up/gets bit by a dog. And here comes the death scream. She's dead, the scream continues.
The loading screen comes up, and Lara is still screaming.
Couple that with the inside of her head and it'd give you nightmares.
Oh, and someone mentioned standing on a little bug and getting hurt. This was in Metal Gear Solid 3. When you're running about underneath Groznyj Grad in the cells, you'd turn a corner and you'd suddenly lurch forward and become poisoned. Turns out on the floor, there's a spider that's extremely poisonous.
He's a handy little bugger though, tranquilize him and throw him at guards.