If, however, you are faced with a more formal occasion and you have to deal with the ranting of some crazed fool in the audience, the best defense from the start is to stay calm. We can’t emphasize enough how crucial it is for you to remain in control. Simply ignore whatever nonsense they’re spouting off - remember, this person is looking for a soapbox to stand on. If the problem persists, you may have to acknowledge he exists, so if you want to shut him up, be polite and firm. Say something to the effect of, "We’ll address all comments and questions from the crowd after I’ve finished speaking, thank you." If that doesn’t work, the situation becomes worse, and the crowd hasn’t told the guy to shut-up, you may simply step back from the microphone and wait for somebody else to do something about it.

Let us reassure you, only in special cases does this happen (politicians mostly, who deserve it usually). If it does happen, we say again, remain calm.