When you know someone is taking a shit, you run in the bathroom during the shit and you yell,
"ARE YOU TAKING A SHIT?!"
and the other person will prob be like,
"GTFO"
and you say in a high pitched voice.
"BUSTED"
then exit the bathroom.
After you complete the task completely, you are now officially a shitbuster.

It’s an acronym standing for Can’t Remember A Fucking Thing. It’s usually used to describe embarrassment at being unable to remember someone (CRAFT moment); going onstage as the lead in the latest theatrical performance and your mind goes completely blank (CRAFT situation); the next morning after a night when you got pissed as a fart and woke up in bed cuddling a traffic cone and a string of fairy lights wound round your prick.

The bathroom version of a ghostbuster. Shitbusters flush any toilet that still has shit in the bowl. Shitbusters that flush leftover urine in toilets and urinals are called pissbusters.