Green’s Dictionary of Slang

1. one who frequents discotheques.

1985		Texas Mthly Nov. 155: If it wasn't for me, there would be no Gilley's, there would be no Urban Cowboy, and Travolta would still be some kind of disco biscuit.
1990		Sassy n.d. 221/3: That song is you at your disco biscuit best.

2. a Qualuude (methaqualone).

1981		Newsweek 28 Sept. 93/1: They prescribe a bottle of Quaaludes, a powerful and popular sedative known technically as methaqualone—and to legions of abusers as ‘pillows’, ‘disco biscuits’ and ‘vitamin Q’ .
1989		G. Cagle Payola! 50: ‘Lude, vitamin Q, disco biscuit, gorilla pill [...] When it comes to drugs, I'm just a precious novice’.

3. (drugs) MDMA.

1991		P.J. O’Rourke Parliament of Whores 118: Who wouldn’t rather have a couple of plump, flaky lines on a mirror and half a disco biscuit than lead the lives these people are leading?
1997		S. Champion Disco Biscuits v: Dennis The Menaces, Rhubarb and Custards, White Callies, Pink Flamingoes, Snowballs, Kinder Eggs, Energizers, Hammer & Sickles, Disco Biscuits.
2001		K. Waterhouse Soho 51: Not that Alex had ever done drugs, apart from Es or disco biscuits as they were known.
2002		London NHS Trust Community Drug Service ‘The Facts About Ecstasy’, In the Limelight 🌐 What is ecstasy? [...] It is also called E, XTC, Adam, Love Doves, New Yorkers, M25’s, Disco Burgers, Dennis The Menace to name a few.
2002		R.G. Barrett Mystery Bay Blues 26: Just because I drop the odd disco biscuit and hit a rave now and again [...] doesn’t mean I don’t like [...] rock ’n’ roll.

(US) a male fan and frequenter of nightclubs.

1989

C. Hiaasen Skin Tight 82: In contrast to the disco Dannies, the mates wore T-shirts and sandals and deep Gulf Stream tans.

amphetamine sulphate.

2000

N. Barlay Crumple Zone 34: Checks me out first like a bint asking him for a wrap of disco powder up the Plastic Coconut in Tottenham.