This is funny I was sure this was early 2000s internet slang before reddit even existed but then I realized reddit got popular in like 2006 which matches with the urban dictionary entries from ~2005 I found.

But then there was this article

The figurative circle jerk emerges by 1972, when the phrase liberal circle jerk time made it onto the pages of New York Magazine in an article about the congressional campaign of Bella Abzug, a feminist activist.

So (un)fortunately not reddit’s fault this time lol. It is interesting though mostly realizing the internet is just the same 3 shitty sites for almost 20 years now holy shit.