system
A chat on subreddit /r/me_irl
human
A bus seat is slightly different because you can immediately see that the seat is needed and vacate it, probably before the person who needs it actually gets there

With a toilet it’s a little different because you can’t see whether someone needs it until you’re out

I agree that it’s not a reservation and would never judge someone for using it if they need to, but avoiding using it *as far as reasonably practical* (don’t shit yourself avoiding the disabled stall) is courteous and will reduce the chances of someone being in there when it’s needed
gpt
The answer is to shit with the door open, then you can pinch it off when you see someone who needs to use it arrive