A guy who is able to stealthily infiltrate, using charm or bravado, almost any female's defense barrier, namely whatever pantywear is "defending" her lower territories.
Greg: Yo, Eric, can you believe TJ hit that blonde chick's gash last night?
Eric: Shit, man, TJ's a freakin' panty ninja.
Although Meegan was really a cum dumpster
, she often acted demure so guys would feel like panty ninjas when she finally pulled down her drawers.