In all seriousness I have two of them, and others may want to add more but I think you can make an argument against most of the others in a long list. I mean, I make games for me the type of games that I would like to play but according to some that might be a bug rather than a feature but I'm starting to digress.
1. "Fix" another person's game.
Now, something someone does might piss you off enough to make your own game. Misspent Youth is a reaction to a game of CyberGen that I ran a long time ago, and it's pretty freakin' awesome. I recently picked up a game that was supposed to be about Ghost Stories in space and it never really got to it, which means that I want to make a game that deals with ghost stories in space, but that doesn't mean I want to fix that game.
Fixing the game means taking the mechanic that someone else did and trying to "fix" it, make those few changes that you think are vitally important to make the game 'more playable.' Which goes into the "fixing D&D" kind of category. Get inspired, get frustrated, get annoyed but make your own game.
2. Not Finishing
This may spill over into personal pet peeve of mine, but you'd be surprised how many people out there think they can do a better job than you do and then never do anything. If you're going to talk to the talk, walk the walk and get the game done. It doesn't have to be perfect, it doesn't have to be amazing, but it has to be done.