In such a setting, begin talking to him as though he was in a shunning contest and was not doingg so well. He can't speak to you: those are HIS rules. You can make him look like the fool he is.
"OK, folks, the shunning has begun, and Bob is pretending to not see my outstretched hand! But how long can he maintain the pretense? OH! Bob has turned his back and is walking away! Let's help him, shall we? Gimmee an "S"... S! Gimmee an "H"... H! Gimmee a "U"... U! Gimmee an "N"... N! What's that spell? SHUN! What's that spell? SHUN! What's that spell? SHUN!..."