A person who lacks the common sense to avoid antagonizing ninjas. A social klutz who does not know how to behave in public. Missing hands or fingers is a sure sign, but not required.
I can't believe that you just ate my BK mini burger off my plate, you are such a ninja petter!
You: Let's wait for the light to turn before we cross.
Me: You are such a ninja petter, there's no traffic.