Once OTB I had an opponent look up from the board & tell me, “I’m announcing mate in 6.” Told him I didn’t see it and wanted to play it out. He got in a real snit, called me a couple of names then went & got the TD. The TD told him, “You ain’t Morphy. Play it out.” The guy sat down and every time I moved, he moved instantly and slammed the piece down as hard as he could then banged the clock (mine, of course) with his fist. What really made me mad was he mated me in six.
So far in 45 years of postal and 2 years of Internet, I've never ran into any really rude behavior!