A Spurs video from the archives. It says the video is from 2007, but I suspect it's actually from 2006, when the team held training camp in France (check out the court -- it has temporary NBA court markings laid over the FIBA lines) and went on to win a championship.
Goofy though he may be, Popovich is not just messing around. He's not only showing an endearing willingness to make himself look foolish, but he's also clearly neutering anyone's ability to ask for superstar treatment.
I especially like it when he asks what he should do if he's cramping up already, and the response is to suffer: