Uh like an actual circle jerk?

It's when a group of people form a circle and masturbate. This also includes when a group of people form a circle and jerk the other person usually to their right.

Circle jerking on reddit is usually the phenomena where reddit comments will breed reddit comments agreeing if it isn't countered quickly enough. You see this a lot in terms of fanboyism or random hatred

Example is how everyone on reddit is hostile to Fortnite, ea games, and Activision. Going so far as to make stuff up about these games and companies.

The circle jerk there is how everyone joins in and beats the dead horse.