bathroom ninja 

A person who occupies a bathroom stall and refuses to make any BM noises until the entire bathroom has been vacated. Occasionally, a bathroom ninja will even go so far as to stand on the toilet seat to avoid detection by other bathroom-goers.

Jacob hid in the shadows cast by the stall walls like a bathroom ninja until the final shitter had left the restroom.

bathroom ninja by timr211 August 15, 2014

bathroom ninja 

–noun, plural -ninjas.
a person who sneaks into restaurant, retail store, or quick mart for the soul reason of using the restroom and doesn't make a purchase.

Manager: Did that gentleman buy anything?
Cashier: No, he was just a bathroom ninja.

bathroom ninja by lookslikelolita September 25, 2008

Ninja Bathroom 

A secreted bathroom, typically in a large and winding house that one can dump like a truck in with enough getaway time to not be caught. Also ideal for hiding.

"Who raped the Ninja Bathroom?"
"Pork and bean night, shouldve been faster. Hey where the fuck is Al P?

Ninja Bathroom by T_low June 12, 2010