If someone's zipper is down, or if they have something on their face, do you tell them or not? Was speaker at lunch meeting and asked why skipping lunch. Told story of how years ago had significant amount of catsup on my face, gave entire presentation, walked around the room, and when leaving found over a hundred people noticed but didn't mention it. No more eating two minutes before intro for me.
Which led to riveting question: if you noticed someone's zipper down, would you tell them? And if yes, how. Answers ranged from no to maybe to depends how well know them to yes. Men said they'd tell men as easily as a woman; and women said they'd tell men as easily as a woman. Consensus that best way to do it is quietly/privately say "your zipper/fly is down" without adding anything else. Also thought if someone said "XYZ" (examine your zipper) wouldn't know what talking about; and expressions about barn doors would be clueless or closer to uncomfortable than direct approach ("your barn door's open", "don't let cow out of the barn").
Real Simple says this: "In many cases, it’s not your place to step in. 'If you're in a large group or the person is the CEO of the company, you don't have to say anything,' says Jodi R. Smith, president of Mannersmith, an etiquette consulting firm based in Boston."
Take it from me, Jodi R. Smith and others - if they're in a large group, and if they're a CEO, it would be really nice/helpful to tell them. Wouldn't you want to know?