Have you talked to "John" personally, had him stay after a moment, etc.? Maybe you can get a sense of whether he realizes he's being disruptive and whether he wants you to help him help with it? My father when he got older, use to tell the same joke over and over but he and my mother set up a system where she'd make a special sign and he'd know he'd told it (something like Carol Burnett pulling on her ear for her grandmother :-) Maybe you can work out a phrase or word with John so it reminds him when he hears it to settle down? My husband has a few phrases for me that help me when I get tangled like, "I don't hear any nouns" and I know to back up and find a subject noun so he can follow what I'm saying :-) Maybe a simple, "I'm speaking" or something will remind John he's out of order.

I'd say from my high school/early college days that he probably admires/has a crush on you? He just doesn't know what to do and is trying to show he "cares". Interesting that he had/found a clothespin in the classroom? I can only think it might have held his paper lunchbag closed or something and so might remind him of whatever woman makes his lunch for him? Far-fetched probably :-) but you might unconsciously remind him of a woman he knows/loves/admires/is "related" to. If he doesn't know how to "start"/communicate with someone he likes, might be the only thing he can think of.