I hate what playing Mafia---video game--almost did to me. After I finished the storyline and was playing Free Ride and what have you, I basically just turned it into "Hunt down as many civilians as you can and shotgun them in the face." I kept doing it so much that I began to glorify it, and when I realized what it was making me do I immediately deleted the game.
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I hate that I had to delete the game, too...it was a great way to work off stress.