but there are many uses, to check your teeth after a copious business lunch, to remove some food from lips... to make sure nose is clean before an important meeting and so on.
nobody will be on the side of reason?
You point out some legit reasons with the teeth and nose and all. But reason or not, you're gonna have people looking at you funny. Plus you can do that stuff in the restroom after you eat. Dudes checkin themselves with vanity mirrors just seems wrong.