To poop or not to poop?

Yeah that's usually not how this works in real life. If two women are having sex, they usually don't need or want a guy to join them.

I would still offer. Theres a one in a million I hit the jackpot, and quite frankly they are having sex in a public bathroom so I wouldnt feel too bad for 'intruding' (note that by 'ask' I mean just say out loud "can i join you ladies ?" or something like that, NOT open the stall or anything actually physical without their consent).