My fave math prof in college once took a considerably long detour to tell us how Jaws was a really great movie (he had just started writing out a HUGE equation, and he said "We're gonna need a bigger chalkboard," at which some of us laughed. And then he talked about Jaws)
He also once went majorly off-topic talking about how he knows more about Canadian geography than American b/c when he was growing up in India his school got free text books from Canada and not the US.
He was an awesome teacher (for much much more than these off-topics. He was a great teacher for Calc III, always giving us insanely hard questions that were just barely within our range, continually pushing us)