Yeah, huh, having read the OP my mind kind of went to "stunned silence" as well. The next thing that comes to mind is that the guy sounds like a bitter jerk who resents other people being in any kind of romantic relationship and tries to poison or belittle them. I don't know, of course, but that's the impression I got. If that's how he's going to treat a total stranger he's just met, I wouldn't feel any need to interact with him ever again.
I was imagining that the person who pointed out that Marty hadn't introduced himself to BF said something more like, "Hey, Marty, have you met Riversong's BF yet?" As opposed to, "Marty, you rude boor, introduce yourself to this young man like a proper gentleman." So I wasn't imagining that person as being rude. Although, now I'm wondering if Introducer knew how Marty was likely to react...