Ha-ha! The one that comes to mind is when I was teaching in college. I asked a mature, stable student to allow me to use his computer to show a DVD I wanted to use for a lesson. He sat on the front row, as all good students do and his computer was handy, plugged-in, booted-up.
I put the DVD in & it wasn't running. A few seconds later, a major porno came up on the screen.. a woman was doing something & I was agast! Students were laughing & howling. A teacher walked by the classroom, his face plastered to the window. I was pushing buttons saying, "turn this off! turn this off!"
Oh it was funny, though.
A male student called out, as we finally (1 minute later) got the thing off the screen, "at least it wasn't a man!"
Still makes me laugh.