I hate the DM that views the group as "my group," or the campaign as "my campaign," as opposed to a collective effort. I despise the heavy-handed and arbitrary style of play (favoring the DM's sense of narrative, or simply his perceived authority as DM) that inevitably results. I abhor the ham-fisted and clumsy efforts that such DMs take to "control" the campaign, such as dictating player character motivations or reactions, or hand-waiving rules on behalf of or against the player characters. I openly deride DMs that openly appeal to their own authority as DM or use deus ex machina plot devices to "keep players in line."
I hate players that encourage DMs like that, directly or indirectly.
Between both players and DMs... I don't like the conflict-aversive nature of many gamers. When a personality conflict arises, most people don't say anything about it. They just stew over it and let it blow up one day, or they let the group dissolve. I do absolutely and unequivocally hate passive-aggressive behavior in game groups.
For what it's worth... I also hate DMs and players that act like I'm the jerk when I actually try to talk through a personality conflict or other issue with them instead of picking a side and getting snotty about it.
