The Boys in the Band (1970)

It's Harold's birthday, and his closest friends throw him a party at Michael's apartment. Among Harold's presents is "Cowboy", since Harold may have trouble finding a cute young man on his own now that he's getting older. As the party progresses the self-deprecating humor of the group takes a nasty turn as the men become drunker. Climaxed by a cruel telephone "game" where each man must call someone and tell him (or her?) of his love for them.