In most grand theft auto games, a lot of cheats include left down right up left down right up. On an xbox or ps2 controller, you can slide your thumb across the directional pad to put these buttons in. If you do this too many times, you'll wear the skin off of your thumb.
Video gamer 1: Hey, wanna play Halo 2?
Gamer 2: No, I have a bad case of Grand Theft Auto Thumb.