Typically working in first-in/first-out order, if you go the bathroom and notice that someone is already using a stall (as if anyone wouldn't notice that earthquake fart), you should politely wait in your stall until that person has exited the restroom before you exit your stall. This order can sometimes be disturbed by speed-shitters and reading-a-freaking-novel shitters. If you're just taking a leak, you do not have to wait.
COPY GUY: I bet it was Ray--that guy eats so much crap he's destined for the brown deluge.
MAIL GUY: Thanks to my good pooping manners, we will never know, and he can keep his dignity.