Extremely old forums meme was if someone posted really quickly while you came up with a reply, you'd see people type something like:
EDIT: Ninja
ninja was used more as a "you said what i was going to say, cunt" rather than just a thread going super fast.
say you wanted to call someone a sick forget for trying to have love with a tuna jar, and as you were writing that another person said the exact same thing and beat you to the punch; that would be a ninja moment.
that wasn't really an exclusive thing to this board too, it was more of forum culture back then.
same with -snip- in quoted posts to remove images so you don't pagestretch and cause the i286 to explode.
another was "Pageloss" - a lot of the time the final post of a threads page would go unnoticed and unread, if that happened then you'd occasionally see that person repost it on the next page.
truthfully, this served no purpose other than showing who was desperate for attention.