In general, speakers shouldn't worry that every questioner is out to get them; this is speaker paranoia. But occasionally a genuinely hostile question will get thrown your way. There is only one way to behave if this happens: Be courteous. And here's another "Never." Never—under any circumstances—become defensive, angry, or snide. If someone deliberately tries to embarrass you, being polite is especially effective. Audiences appreciate fair play and good manners. They will automatically reject the person who is making trouble and be on your side—if you continue to be polite and unruffled.
If you are dealing with a tough subject and expect a hostile audience, asking people to state their names, companies, and so on, can reduce the amount of questions, because many people do not like to volunteer this kind of personal information. This tactic can work at large rallies or in groups where people are not already acquainted.
Being polite doesn't mean you have to be a patsy. If the questioner is out of hand, you can cut him off. If he is especially provocative, you might consider the kind of reply General Hugh Johnson used occasionally: "I'll answer any fair question, but I won't answer a loaded question like this one."