According to definition-of.com:
A T-Room, often referred to as a "tea room" in gay slang, is a men's restroom used for anonymous sexual encounters between men. These locations provide a space for casual, unscripted sexual activities, often in public spaces like parks, due to societal stigmas and legal constraints surrounding same-sex relationships. The term is a euphemism, reflecting the discreet nature of these encounters and the historical context in which they emerged.
As recently as last year, I caught someone in the men's room at a department store trying to engage in gay sex. He was taking forever in the one and only toilet stall with the door cracked open and sitting there masturbating. A line was forming to use the toilet. I really needed to use the toilet, so I just said "Hurry up, stop wacking off, there's guys waiting to shit" and the guy quickly left.