I start splitting hairs. Asking questions like "In what sense?" and "What's at stake if somebody is wrong?" If "right" or "wrong" is about smthg without consequence, I stop hairsplitting and just agree.
If not, I continue to assess the situation. Is it ok to let everybody think they're right, even if somebody is wrong? Is the "wrong" person accidentally wrong? Maliciously wrong? If I question their wrongness without the backing of some authority figure and/or the group, will they try to take their indignation out on me by trying to take smthg from me? Will they take it out on somebody else? Who?
After this process, I'll take any number of actions, depending on what the answers to my self questioning are. I'd rather not discuss them right now, tho. It's dinnertime and I'd have to draw a frikkin chart to cover all the possibilities and contingencies that typically go through my mind when I'm reasoning my way through "Who's right, who's wrong and what should we do about it?" It all happens inside my head in under a minute.