Huh. That happened to me today. It went like this:
Me: what did one cell say to his sister cell that stepped on his toe?
Person-with-no-humour: what?
Me: mitosis (containing laughter)
Person-with-no-humour: ...
Me: you didn't get it did you...
Person-with-no-humour: eh... No.
Me: let's pretend this never happened
Me: what did one cell say to his sister cell that stepped on his toe?
Person-with-no-humour: what?
Me: mitosis (containing laughter)
Person-with-no-humour: ...
Me: you didn't get it did you...
Person-with-no-humour: eh... No.
Me: let's pretend this never happened