I open threads that are boring, uninteresting, maudlin, excessively Anglocentric, overly esoteric, or populated by people with bad dispositions. Mind you, I don't do this intentionally, it just happens.

Sometimes I'll accidentally open an interesting thread, usually after everyone else has already gotten tired of it. So, I'll compose a witty response, post it, and watch the thread drop off the page like it has a 500 lb. kedge anchor attached to it.