afaik: short for janitor, and intended to be derogatory when used towards mods or admins.
I think it might have been popularized on 4chan? Idk that’s the context I’ve seen it in most and it fits their MO of shitting on people for working jobs or contributing to society at all.

Seems like a pretty shitty attempt at an insult imo tho, cuz a mod and a janitor basically do the same function (cleaning the shit so nobody else has to deal with it, ensuring the place is actually nice for users) and both are critical for public places but underappreciated/underpaid.