Ignored them. Totally ignored them. They want attention, and even negative attention is still attention. Remove the payoff. Don't look at them, don't respond no matter what they say/do. If necessary, simply get up and move. Best if you discuss this with your group members beforehand -- if someone intrudes and behaves badly, what do we want to do?
Some societies have used this to good effect. If someone misbehaves, he essentially disappears. No one will speak to him or interact with him until his punishment period is over.
Expect the person to respond first by escalating the behavior in an attempt to get attention, but if you refuse to acknowledge him, he will eventually give up.