While sending an email might be a good solution, I don't think it is a good idea to be confrontational about it. I think you need to make them see that they've been behaving like immature idiots, but without it escalating into a confrontation.

I think all reasonable people will be on your side if you handle it well. I like the idea that someone else came up with of posting this thread up on the noticeboard. That might embarrass them into shutting the fuck up and make them realise what a bunch of ignorant, immature dicks they've been :)

He doesn't have to be confrontational at all.

An e-mail in a softer tone, stating the facts and that it hurts would be enough. He should mention HR in there too.