Chicken Sex on Bamrung's Day Off — Christopher G. Moore

The story is from the collection titled Chairs.

A waiter from the old Thermae in Bangkok is surrounded nightly by hundreds of women who sells their favors at night. When he is called upon to help one during the day he finds that the relationship, his perception and the rules of the game are much more complex than he ever could have expected. Outside of the coconut shell he finds a new world to which he must adjust.