1. noun - cockblocking maneuver involving the unauthorized entry of an unclothed male into a room occupied by two or more people currently hooking up or having intercourse. the 'ninja' employs dramatic body action (e.g. jumping into a room with wide open arms) and a verbal cue (e.g. "naked ninja!")
Additional Notes: It could in theory be done by a female but such action might be desirable.
2. verb - the act of being a naked ninja
Step 1. Remove all clothing
Step 2. Find a bedroom where two people are hooking up or having intercourse
Step 3. Subtly determine if the door is unlocked, if it is unlocked go to step 4, if not, go to step 3a.
Step 3a. Unlock the door by any means necessary while preserving the element of surprise
Step 4. Throw the door wide open
Step 5. Leap into the room with a signature body gesture and scream "naked ninja" ensuring that your genitals are in plain view.
Step 6. Run like Hell