text: I'm not sure of who invented "that rule", but think of it like this:  When you burp, you shouldn't just belch out and act like nothing happened, you should say "excuse me".  It isn't really rude to "fart" because man or woman or whatever race you are, we are all humans and that isn't unusual, but if you do fart, you should say "excuse me" or "sorry", instead of laughing at it and doing it to aggrevate.