Here's some of the kinds of stoners I hate the most:

-Moochers. I know they'ved been mentioned, but it's one of my pet peeves.

- Stoners who think they know everything or think they're better stoners than you because they have more "experience". I actually have a friend who thinks he's better than anyone who hasn't been smoking as long as him, yet he acts like a total jackass when high.

- Stoners that hog the joint/blunt/smoking apparatus because they think you'll get more than them. (that's why I like to set limits on how much to toke per turn).

Other than that, not much bothers me. As others have said, accidents can happen when sharing weed and is not worth getting angry about those accidents, especially if the person is normally a good stoner.