Somebody Boil Water!

I'm home sick with a case of joke theft.  I understand that this is a common ailment among comics, but it doesn't make me feel better. Jokes aren't just written; they're labored over and delivered. Once you create them, you can't help but feel proprietary.  It's bad enough when someone steals a joke and you hear about it. I had someone steal a joke and recite it right to my face. I didn't say anything to him because I'm too inexperienced to know the proper etiquette, but I mouthed HE STOLE MY JOKE over and over again in a silent rage.
Comedians, at least new comedians, often listen to other comedians with half an ear; either we're concentrating on our routines preparing to follow someone on stage or  dissecting our routines once we sit down and someone else is up.  The mind is a strange place and it is conceivable that one can hear and process something without listening attentively. I know that feeling when an idea hits you like a thunderbolt and you have to pull over on the highway and write it down. The problem crops up when the idea wasn't yours to begin with and you honestly don't realize it. This happens to people of good will.
This really felt different. The topic and the punch line were the same. There was a slight distinction, but not enough. I don't know this guy and I have no idea if he's a good citizen or a dirtbag. I would hate to think that he would have the mens rea to pluck a joke from my arsenal and make it his own. No one can convince me that imitation is the sincerest form of flattery in this instance. I'm tickled if someone orders the same pair of sandals from Onlineshoes.com or gets a little boy haircut. No, this was not the same.
Here's the rub, though (attribution to Shakespeare).  I have an inkling that joke theft accusation in the comedy community is almost as uncool as joke theft.  One possibility is that  I could take a very tactful approach and tell my thief that I'm sure that it was wholly inadvertent on his part,  but I wrote that joke and told it the last time I saw him. The problem is he may get defensive, try to convince me that he wrote the joke while he still was in utero, and smear me in this small community.
I think the first order of business is to calm down and not do anything right away. I know from 55 years experience that when I act out of anger, it drowns my message and I don't get the result I was seeking. It may take some time. Right now I feel like someone stole my baby.