metacomment

A comment in an online forum or discussion board about a topic that is, itself, about a comment or the author of a comment rather than the topic being discussed.

Metacomments typically occur as a series of negative personal comments between participants and tend to derail the topic of conversation, descending into chaos (or brilliance, depending on your perspective).

Person 1: I thought the movie was boring. And the lead actor is way too unattractive to take seriously as the love interest.
Person 2: Your boring and unatractive.
Person 1: It's "you're" and "unattractive" dumbass. Learn to spell.
Person 2: Oh, sorry. Is this better? You're unattractive.
Person 1: Nice one, bitch.
Person 3: It was much better than Cats. I'm going to see it again and again and again.
Person 1: What?
Person 2: Huh?
Person 1: Fucking dork.
Person 2: Yeah, prolly lives in his mom's basement.
Person 1: True. And you should "prolly" learn how to spell "probably" too.
Person 2: Ugh.
Person 4: What's with all the metacommentary? Can we get back to talking about the movie?
Person 1: No.
Person 2: Shut up.