My favorite to this day remains what the mother of the wife of a friend of mine assumed
So you are working with computers? Could you take a look at my washing-machine
to be fair it was a modern digital edition ;D ... still I have to smile every time I think about it.
and the all time classic:
A: You are a programmer, right?
B: Yes.
A: I have a problem with my computer, could you help?
B: Depends on what the problem is,
what kind of computer do you have?
A: a grey one
B: .....
^^