social rules concerning embarrassment

Have you ever been someplace, like say, oh...work, and you've just finished some food item that may be a pastry or scone that has some messy fruit quality about it, like say, oh, I don't know...blueberry? And you have this nagging suspicion that maybe fruit or more likely a stain from the fruit might still be on display on say your face? That suspicion grows and of course you're sure that no one will tell you, because that's part of the social rules unless it's a real friend, then they'll tell you. I don't believe that you usually have real friends at work. An example, one afternoon some months ago I prepared at home for work, showered, got dressed as usual, and went to work. I made my rounds checking in with different folks at work. I was there I guess about half an hour/45 minutes and after coffee decided it was an appropriate time to hit the little workers room. Upon stepping up the plate, as it were, I discovered, ah no need to unzip, it's already been taken care of! Hey! Wait a minute...I don't recall doing that at any point between now and when I got dressed. Dammit! Dammit! Dammmit!
Can somebody tell me why no one tells you when you have a 'situation'. If the panty section of a woman's panty hose gets exposed due to gross clothing negligence, no one says anything. Why? Of course, that's actually kinda funny now that I think about it.
Oh, all clear on the blueberry. All that worry for nothin'.