Olaf the Stout
Hero
At the risk of going off topic, having enough of a story outline planned out to have villains ready 12 levels ahead is not automatically railroading. There's plenty of room between "complete sandbox" and "linear railroad" for a good, plot-intensive campaign that still allows substantial player choice.
Back to topic...
There are certain games I'm not interested in playing, but if a group of good friends really wanted to, I might at least give them a shot.
I won't play in a game where role-playing (things like "speaking in character") is forbidden. I'm not interested in a minis tactical game masquerading as an RPG.
I won't play with people smoking inside. I used to, and I can't tolerate it anymore.
I won't play with people who are drunk or stoned. A beer or two is one thing, but if it starts impeding your ability to take the game seriously--or, alternatively, causes you to take it too seriously--then it's impeding my ability to enjoy the game.
I won't play with people whose only goal in playing is power-trip fantasies, or venting socially repugnant fantasies. If you want to run an evil campaign as a change of pace, that's fine. If you want to do it so you can linger over your description of rape, I'm gone.
There are probably others, but those are the ones that come to mind at the moment.
I was going to post mine but this comes pretty close to what I was going to post.
I hate smoking but if one of my players wanted to smoke they could do so as long it was outside. Thankfully none of my players smoke so this is a non-issue.
Drinking during a game and being drunk during a game are two very different things. I have one player that occasionally brings a couple of pre-mixed bourbons to the game. Another player has had a couple of beers during the game when we had a full game session. None of the players have ever gotten drunk though. I don't imagine that would make for a very good game.
Drugs are a no-go for me.
The last point that Mouse brings up is thankfully one that I've never come across. I would be out of the game (or booting players out) if it did ever occur.
A couple of others that I would add are:
DM's playing favourites.
That's great that you're friends or boyfriend/girlfriend outside of the game. I can deal with that. However, if friendships/relationships outside of the game lead to favourtism in the actual game I'm outta here. I have been the DM for basically the last 3-4 years so this hasn't really come up.
Players that want the DM to change the rules to how they are used to playing.
I had one player that didn't like some of the 3.xE rules and wanted me to change them. Some things, like moving spells back to their 3.0E durations, I allowed. Others, like not allowing bad guys to have critical hits, I denied. However, once I allowed a couple of changes I was constantly bombarded with his gripes about the 3.5E rules and how if I let him change X the game would be better.
Playing D&D is fun. Constantly wasting time arguing about changes to the rules is not. Never again for me.
Players that constantly argue with the DM over rules interpretations during session.
I admit that I'm not always right. Sometimes DM's make mistakes on rules during sessions. I'm happy to have a brief discussion about a rule during the session but once that discussion is had and I make a decision, it is done. I'll happily discuss it out of session but for now you'll just have to abide by decision, even if you think it's wrong. I've wasted too much time arguing rules interpretations during sessions to put up with it any more.
Those last 2 no-goes are just due to one bad experience I had with a player. However I won't be making the same mistake twice.
Olaf the Stout