What's He Doing in There? — Fritz Leiber

The Professor was congratulating Earth's first visitor from another planet on his wisdom in getting in touch with a cultural anthropologist before contacting any other scientists (or governments, God forbid ), and in learning English from radio and TV before landing from his orbit-parked rocket, when the Martian stood up and said hesitantly, "Excuse me, please, but where is it?"

He was asking directions to the loo, as it happened. It was the Professor's Wife, always a perceptive hostess, came to her husband's rescue by saying, "Top of the stairs, end of the hall, last door."

Oddly enough, it was the start of a puzzling and all but unspeakable misadventure. As it were.