Green’s Dictionary of Slang

bull session n.

also bullshit session
[bullshit n. + SE session]

1. (US) usu. of men, a period of sitting around, gossiping.

[US] letter in K.F. Cowing Dear Folks at Home (1919) 7: Generally, in the evening, just before taps, we hold ‘bull’ sessions.
[UK]P. Marks Plastic Age 77: Night after night the students gathered in groups in dormitory rooms and fraternity houses, discussing football, football, football; even religion and sex, the favorite topics for ‘bull sessions’ could not compete with football.
[US]J.T. Farrell Gas-House McGinty 18: I’m gonna take a little walk and keep away from the bull session.
[US] ‘Whitman College Sl.’ in AS XVIII:2 Apr. 154/2: sling the bull, bull, bull session. Closely related terms [...] heated discussion.
[US]H.A. Smith Life in a Putty Knife Factory (1948) 206: Once every month or so Fred [...] creeps off into the wilds of Queens for a bull session involving his good friend Alton Cook and myself.
[US]J.D. Salinger Catcher in the Rye (1958) 174: If you were having a bull session in somebody’s room, and somebody wanted to come in, nobody’d let them in if they were some dopey, pimply guy.
[US]W. Wilson LBJ Brigade (1967) 38: He makes us fidgety, he wants to have a college bullsession.
[US]P. Thomas Down These Mean Streets (1970) 15: It was better to play mysterious with the guys at bullshit sessions, just play it cool as to who and how you copped.
[US]L. Rosten Dear ‘Herm’ 100: They do not stall around about hitting right to the gut in our ‘bull sessions’.
[US]S. King Christine 20: They were ready to take part in an all-night bull-session on the space programme.
[US](con. 1930s–60s) H. Huncke Guilty of Everything (1998) 280: I would have a weekly consultation with a psychiatrist but it was little more than a bullshit session.
Kennedy & Davies Boots of Leather (2014) 199: [of lesbian women] It wasn’t until later that she got into bull sessions about such topics [i.e. having sex].
[US]S. King Hearts in Atlantis (2000) 446: Save that language for your bull sessions.
at [Internet] The Dakota Bull Session is an annual reunion of all military veterans.

2. (US black/teen) police interrogation [plays on bull n.5 (1)].

[US]P. Crump Burn, Killer, Burn! 106: De bull sessions those coppers hold in them stations are back-breaking.