No doubt you know that the Queens' Guards who protect royal residences in Britain, rarely change expression regardless of attempts to make them crack.
One guy (an American guy named Yankel) just managed to make a Queens' Guardsman crack, however. Surprisingly, a running made-up monologue about going to school with the guy did the trick.
I loved how the guardsman turned bright red after he grinned in spite of himself.
(Click ahead to :45 to see the guy start making stuff up about going to school with the guard.)