I cannot understand someone piling on after it had been already heavily downvoted
I vote down when the post is of a kind I don't want to see here, without regard of the post's current score. This seems to me as a more sensible voting pattern than the obvious alternative and I hope I am not applying it alone.
(Disclaimer: I haven't downvoted this post.)
I'm not sure that's actually more sensible, given that upvotes and downvotes aren't shown separately (does +3 means three people want to see more comments like that and everyone else is indifferent, or does it mean seven people want to see more of them and four want to see fewer?). If they were I would do that too, but right now I mentally assign each post/comment a “deserved” score and upvote/downvoted if the current score is below/above it.
I think we could apply the lessons, anyway, but Munroe might have our community in mind specifically. The alt-text refers to emotional biases. I'm just curious if others got the same impression.
http://xkcd.com/1112/