The trick here is to discuss this out of context away from the session. If this person is a friend and you meet them socially outside the session context, try striking up a conversation about how much you enjoy playing in sessions and what it is you enjoy. No need to direct it at his negative behaaviour - if the guy has any cop on (although this may be in doubt from the behaviour you've talked about) he'll probably realise that you're trying to tell him something without being antagonistic about it.

The alternative (i.e what I usually do in these situations, unfortunately) is to wait until he really annoys you some night and lash out. The results can be quite ugly. If it really getting to you, you need to say something, but the calm subtle approach is preferable. If this fails you'll probably need to take a more direct approach, but try to do it early in the session before he has got you really annoyed.