Prick (n): (vulgar slang) A penis; a man regarded as stupid, unpleasant, or contemptible.
I've typically heard it used to describe someone who is a stuck up or self righteous asshole. I'm not sure what additional meaning you are assigning the word, so here is my advice:
Cut the passive aggressive bullshit. Passing notes? Are you serious? Next time you see this guy, tell him (to his face, do you understand?) "Listen dude, when you called me a prick last time it totally killed the atmosphere for me. I mean, it didn't fit with the RP or action at all. Did I piss you off or something? It really bothers me when people use that word and I just want to know how it can be avoided in the future." Since you are probably not the confrontational type, you would clearly have someone else within earshot to intervene if the guy decided to be a dick about it.
Also these lines: " If it happens again don't expect me to ignore it and write a civil message here."/" I'm sure I've had more experience dealing with bigots than you have being bigoted"--actually the whole message really makes you come off as a prick. Here's a better message for you:
"Last night one of you called me a prick. Some of you may not know that I am, in actual life, a (whatever prick is slang for, I'm assuming gay but maybe it's raging cuntbeast), and I find the use of that derogatory term to be offensive and inappropriate, whether or not its use is directed toward me. I try to show respect for all of you during our sessions (whatever you call them) because I want everyone else to have a good time, and only ask that you show the same respect for me. I don't want an apology or an excuse; I just want to LARP and have fun without worrying about the shit I deal with every day in my real life, same as you."