Sometimes I get to be the observer of the wacky instead of one of the participants. My only participation in this one is it occurred in a tournament that I directed. I have changed the names to protect the guilty. Let's just say it was a case of an adult acting like a kid against a kid.
The position may not be 100% accurate since I'm recreating it from my head, but the pieces crucial to the play are correct. "Mr. White" had just played Rh3 with the vicious threat of Qxh7#. He was sure that young "Mr. Black" had no defense against this mate threat. When Mr. Black imediately played g5 Mr. White figured he was just giving up by allowing the mate. As soon as g5 was played Mr. White plays Qxh7+?? and says "Checkmate". Mr. Black says nothing and plays Bxh7!!
Alas, Mr. White fell into "Do as I say, not what I do" mode. I know that he has told his students to double check their move before making it. Also some things are best left unsaid. Checkmate is one of those things.