Back in the olden days of Serebii, around the year 2008, there was one of the biggest threads alive there, ironically a thread about Competitive Battling.
I was one of the regular and top posters in that thread, and had mustered up 178 posts in the thread with threats like chores, school, homework, and the like clogging up my life. But I'm getting off track here.
Quite frequently, someone would be finishing up a post when I started typing, leading me to have another post to reply to. I would signify that I missed one with "Edit: Ninja'd" in some form or another. This happened a lot, to the point of being a running gag, as if I was "bait" for being "Ninja'd". At first, for some reason, everyone kept adding the Japanese honorific suffix "-chan" to it (Another joke at how sometimes I can be rather... effeminate, perhaps), so that stuck for a while, until no one could be bothered typing the full name, so they dropped the "-chan". Thus, the name Ninjabait was born.
Hooray for pointless backstory.