Houserules that aren't in writing. If they aren't in writing they should be short, unless you rewrote spells instead of banning them. This isn't counting stuff like blocking drown healing or unwritten houserules you can tell me verbally in under a minute. Double points against your game, if you spring bans on me rapid fire as I point out potential issues your existing houserules may raise.

Ludicrous DMPC's.

The game not being what it says on the tin. If I make a dirty cop Deputy for an Old West game; I have no interest in getting Rip Van Winkled to a modern setting. I know good games can come from curveball like this, but I had my fill in my teens/early twenties. At this point I feel I'm a mature enough roleplayer to play a fish out of water without being surprised OOC.