My tolerance for bad game design has dropped sufficiently over the years that I now quit playing when the culmination of flaws in a game get high enough that it frustrates me enough to turn the game off in a rage. As long as I never hit that point, I don't get tired of a game until it's just too tedious to keep playing it. And that can take a very long time indeed. No exact numbers for you, because as has already been pointed out, it varies immensely from game to game.
Sky Render - Sanity is for the weak.