We had to listen to a long, boring, meaningless management conference call some years back, and a buddy and I were in my office listening to the call and playing bullshit bingo. After a few minutes our boss, the VP of Marketing, wandered in to find out what all the hilarity was about, and caught us in the act.
We shrugged and smiled sheepishly, after which he went back to his own office and prepared for his part of the conference call. As soon as they turned it over to him we heard him, over the phone and to everyone, announce that he'd caught two nameless employees playing bullshit bingo and they'd better not be doing it while he was presenting.
Best boss I ever had.