Green’s Dictionary of Slang

(US) of boys or men, to indulge in group masturbation; thus circle-jerker, one who joins a group of masturbators.

1969		P. Roth Portnoy’s Complaint 196: The old circle-jerker himself.
1986		L. Heinemann Paco’s Story (1987) 13: Circle-jerking our brains out. Our forearms just a-flying, James, our forearms just a blur.
2016		D. Whish-Wilson Old Scores [ebook] The circle-jerking, the smell of spoof everywhere, gash on everybody’s minds.