A weed ninja is someone who, when under the unfluence of pot, takes on the persona of a ninja. He thinks himself to be super sneaky but he is not. A weed ninja is known to tell people via text or bb messenger, that he is infact, a weed ninja.
When that guy gets high, he becomes a total weed ninja
A pot head, with enough years of experience and ability to camouflage him(her)self as a non-stoner amongst coworkers and/or society.
Dude! Did you know Joe, from work, gets high every night?
No way! I could never see him being a stoner.
Yeah man, he's such a Weed Ninja.