One who can masturbate/masturbates everywhere they have gone/are without fear of being caught, with any object, without being seen, heard, or others having suspicion of the action of masturbation, any where, any time, and any place.
Student #1: Hey man, I whacked off in biology today.
Student #2: HOLY HELL! Did you get caught?
Student #1: Hell no I didn't, I am a freaking Masturbation Ninja.
Guy #1: I jizzed all over my friends moms bra last night while he was in the same room.
Guy #2: What!? He didn't see you?
Guy #1: Shit no, he was sleeping.
Guy #2: Good thing you're a Masturbation Ninja.
Guy #1: Damn right.