What did the girl say to the man with a moustache?
I moustache you a question.
What did the girl say to the man with a moustache?
I moustache you a question.
This is a classic pun-based joke. The humor comes from the similar sounds of 'moustache' and 'must ask.' The girl is making a play on words by using 'moustache' in place of 'must ask' to create a humorous question.