I've been teaching college physics labs for three years. The funniest thing that I think ever happened came right after I announced that the last day's report would be a "turn in before you leave" worksheet (rather than a formal report). One of my male students - who was friendly with everyone - came up and gave me a gigantic hug, then a kiss on the cheek, very loudly and with pomp. My eyes must have looked like saucers, as I had no idea what to do. He gets halfway back to his desk - pauses, half turns with a mortified look on his face - and asks:

"Was that sexual harassment?"

I replied: "...little bit?" - just to watch him go green. And then we had a nice laugh.