A third party who "ninjas" their way into a conversation they were not originally a part, usually with a comment which mean they have been eavesdropping for an extended period of time, like a ninja striking in the shadows.

A person with an outwardly dominant, masculine, or aggressive personality, but who also enthusiastically takes on the submissive or "bottom" role in the bedroom.

One makes a single random comment in someone elses conversation, which ends up killing it and making it awkward for everyone else. This is similar to a ninja swiftly killing a target then exiting.