A person who is unbelievably quite when using a restroom.
Hey man, have you ever notiched how Zack is total toilet ninja?
Mainly corporate personell who go to great lengths at avoiding being seen taking a crap at the workplace toilet
" Hey Bob I felt something whiz by me while I was taking a piss, weird"
"Oh that was most likely Phil, he doesn't like people seeing come out of the crapper, he's a toilet Ninja"
When a criminal tries to dispense of evidence in a restroom, this same-sex modern-day hero follows the offender and physically prevents any further crimes.
This lady was caught shoplifting and, in a panic, ran into the restroom to try and "flush" the evidence, but Katy, the same-sex security guard, and modern-day hero, followed the alleged criminal into the stall, secured the prisoner, and saved the day. Katy is a toilet ninja.
Someone who makes it to the toilet just before you do
'I was going to to toilet and just as I got to the door, Jack rushed in before me!'
'Ah Jacks a Toilet Ninja'