An undesireable person, place, thing, or idea.
Have you tried those chili dogs with M&Ms? That shit is bad ninja.
by jseale1978 October 28, 2003
The variety of stealthy person whom is not very stealthy or sneaky in any way, shape or form and almost always gives away their location, but somehow is never caught.
Jessica Rabbit is a bad ninja, but shes hot!
by Dart Guy July 13, 2006