A person with incredible stealth in regard to their pooping skills. They relieve themselves without a sound or smell, potentially even carrying around an extra pair of shoes to ensure nobody detects them post poop.
I didn't even know someone else was in the can with me until I was washing my hands and saw his feet, sneaky ninja pooper!
A stealthy ninja who poops in the toilet while someone else is using the shower. The ninja pooper then leaves it there with the lid open and exits without making a sound. They are now perplexed at whether they forgot to flush or even went poop at all.
While someone is using the shower, a ninja pooper silently walks in and takes the browns to the superbowl without them knowing. You then proceed to exit the room without flushing to confuse the other person as to whether they forgot to flush or even went poop at all. Priceless.