For me, it was Tetris. I played that game so much when I was in my teens that I used to dream about pieces falling into place. In real life, I saw Tetris pieces falling into the open spaces in the background and in some cases, open spaces in the foreground (like if a girl had her breasts somewhat exposed).
Now I come to find out that Tetris actually helps people with their addictions
. Funny to see a game to which I had grown addicted can now heal my addiction to anything but itself. What a conundrum.
In all seriousness, it's a really fun game and I won't uninstall it because it's just that good.