mine's kinda dumb
It's got about 4 meanings by now.
Lol. When I was in high school i was one of the bigger guys in terms of physical size, but I was always quiet and extremly easily overlooked in terms of personality because i didnt like making a scene. A few people began to call me ninja because i'd be randomly in a spot talking, something would happen to a buddy and I'd be there before anyone knew what was going on.
Second version came from my pool play/gambling attitude I suppose.
I got caught wearing a goofy green tee shirt, couple of guy's started up jokes about me being a turtle, i laughed and told em the only way I was a turtle was if I happened to be one of the teenage mutant ninja turtles [ god i'm showing my young/ old age to some people and I feel dumb] and one guy around the group just laughed and laughed for a good fifteen minutes and stood up. I asked why he'd laughed that hard and he just grinned ' Well you're more like the foot, cause i've watched how gamble and you might as well say Ninja vanish' and throw your cash away.
N33njah was just a variation that I made due to people taking ninja and other things on various other forms.
So yeah mine's kinda dumb, but it's stuck.