Green’s Dictionary of Slang

(US) a drink that resembles whisky (and charged as such) but is in fact cold tea; served to the female companion of a man, or homosexual customer, who has entered a club in the hope of sex.

1947		F. Brown Fabulous Clipjoint (1949) 66: There are plenty of places where they’ll buy a girl all the drinks she wants. And they won’t be B-drinks.
1953		This Week 26 July 7: And a gal that’s good with the B-drink tricks can run it up to two hundred or three hundred dollars.
1965		K. Marlowe Mr Madam (1967) 24: When I was the most successful B-drink hustler in the business, it was because of loneliness. [Ibid.] 100: Every B-drink served you has a star on the stirrer. You break off the top and save the star [...] Then at the end of the night you turn these in to the bar. If it’s a Brandy it’s two stars. The bartender gives you a quarter for every star you have at the end of the night.