Much like the homewrecker, a threadwrecker interferes with the natural flow and order of things, e.g. a thread of comments related to a post on Facebook.
That jerkwad is such a threadwrecker on Facebook!!
Post: JANE DOE is deciding between pizza and mexican food for dinner.
NJ: Oh, I would def have pizza!
ST: Have you tried Jose's Cantina? Awesome?
JW: Hey Jane, is your grandmother out of the hospital yet or did she die already?