I think originally, he just said he was "crashing the poll", but there are a lot of readers of Pharyngula, and the results always tend to be a bit like when fark or whatsit do this kind of thing. So people started calling what was going on "Pharyngulating", I guess as a pun on "calibrating" or something?

Also, I've never seen PZ, when explaining why he posts links to polls, not point out that online polls are easily hijacked and also kind of stupid in that the people running them often point to the results as being conclusive evidence for whatever. There's a very recent post on his blog concerning the matter, actually. Not to say it isn't trolling, though. It is.