Place it at the end of a prank setup, after the victim reaches the restroom, then follow it with the Shocked Meme Sound for the reaction and the Oh No No No Laugh for the payoff.
About this sound
This is a roughly five-second human scream, a single drawn-out AAAAHHHHHH that sounds as if someone has just let out in a public restroom. It lands as startling and awkward, funny because it is so out of place, and it works best when the listener does not see it coming.