The word bathshroom contains the words "bathroom" and "mushroom." These fungi appear in the most discreet of corners, usually in bathrooms where moisture and mold collect and sprout colonies of the most decrepit kinds.
You know you have stepped foot in the nastiest of lavatories when you stumble upon some tile fungus. "I swear I saw bathshrooms growing in that bathroom while I was taking a leak. Somebody get these people some Mr. Clean!"