A person who looks and behaves like a completely normal person and is typically not physically imposing, that actually has profound skill in the martial arts without anyone knowing of it.
So I was walking home sort of late last night with Dan when four guys jumped us! While I was cowering on the ground I heard Dan make some Asian noises and a bunch of thuds in quick succession. Then there was silence for a few seconds followed by the sound four bodies hitting the ground. It turns out my brother Dan is a closet ninja.