Mostaza does not mean mustache.
My co-worker, Antonio, had been on vacation for two weeks.
Upon his return, I saw that he had a new mustache.
I was learning Spanish, so I exclaimed, "Tony, ¡me gusta su mostaza!"
He replied, "You're crazy", because of course, mostaza means mustard.
Tell us your best stories!
(My thanks to ingirumimusnocte for the discussion idea.)