Many years ago I was handed a floppy disk by someone. When I returned it to him, I informed him about the Form virus that I had found on the disk. He then went around telling people that he had gotten a computer virus from me.
Been there so often it's not funny. My most memorable moment was when a supervisor called me saying her computer screen "all of sudden went all squiggly". When I got there I simply removed the magnet she had placed on top of the screen and the problem was solved. She was so impressed she called me at least twice a week to solve anything she was confused about - that included a squeaky chair.