[diebitter]

You could try this:

You: "you remind me of a minge-eater."
Him: "What?"
You: "Sorry, just reminiscing. Used to know a woman who had the same personality and accent as you. She was from Calcutta, but raised in England, and talks just like you. Minge-eater she was called [ie Minjitta]. You just remind me of this particular minge-eater, that's all."

If he wears this, you could call him minge-eater from then on as a pet name?

ehhh, maybe lame, not sure.

EDIT: Alternatively, find out something about him and make double entendres that can be interpreted innocently, but make him sound gay/retarded/stupid if not interpreted innocently.

Eg, if he played rugby at school, you could say stuff like 'I bet you had great fun beating off all the other guys and scoring, huh?'

As long as you don't laugh or give away you're taking the piss, he could well be nonplussed by it and ignore it. You could have enourmous and ongoing fun with this approach. I'm sure OOT could come up with lots of suggestions if you can get some background about him and post it here.

(ps. If it's Richard Dawkins, you can STFU and live with it).