For what reason would a guy ignore you on IM?

Well he might have his computer go online while he isn't there and that might be the reason why he hasn't sent you a message on IM. The reason it keeps going on and off might be cause his net connection is not good. On the other hand if he really didn't want to talk to you he might of just deleted you from his contact list and blocked you but he didn't which means he wants to talk to you but he just isn't sure what to say cause the last time you two met it was a bit weird as you have suggested.

Well, number one, did you ever consider that maybe they weren't even on their computer at the time? I personally do this all the time as a form of answering machine when I'm away from my keyboard (sometimes for the entire day).

But if that isn't the case, there's always calling him or talking to his friends and just flat-out asking him what's going on and how he's feeling. Yes, to you you may be scared because you think it'd make things worse, but it'd be better to get your facts straight than to sit there and let it continue to eat at you like it apparently has.

If you were with your friends then I wouldn't call that a date. A date would be just you and him alone, but anyway, I don't think he hates you. Call him or something and tell him you are sorry for what happened and you hope it doesn't cause any weirdness or anything. Once you do this see how he acts. Don't be too pushy, but definitely call him and say you are sorry for that episode, I mean after all you can't help it. Then lay back and let him make the next move. If he doesn't then move on. Or ask him to go somewhere with you ALONE (no friends!) and talk to him.