I have had sex once in a public toilet and we were in there a loong time. It was at a swimming pool where a friend was having a 21st party. Of course, everyone wondered where we were and why we conspicuously walked out of the Gents toilet 1 minute between each other. Damn good fun that was...
Not the same as a dressing room... but maybe it had the same exciting feeling.. of people walking in and out of the toilet not knowing whats happening inside the cubicle.