(sort of a follow-up to my past posting...)
If we do our job right, then there should be no such thing. Conducting an audience needs analysis prior to your presentation is critical. This helps to uncover hot buttons, taboo topics, burning fires, etc. BEFORE your presentation.
If, on rare occasion, you are chosen to deliver bad news in a crowd (poor form, bad news should be delivered in small groups or individually), then be authentic! That's the key. It is okay to say that you are not pleased with the situation either. Most adults know that life is not fair.
On the other hand, if you encounter the "sniper" or the person who is just out to be a jerk, then try one of these responses:
1. "We do not have the right people in the room to have that discussion today." (Being honest, of course.)
2. "That's an interesting idea, one that I need to give some thought to, and I'll get back to you." (And then move on.)
3. "That is out of scope for this discussion. Allow me to place that on our parking lot (list) for another time."
The idea is take a moment to acknowledge the person's discontent and then move on with the agenda. Never, ever, argue with anyone in your audience, unless the person is viciously harassing you or someone else. Your audience will admire your composure under fire.