Green’s Dictionary of Slang

Britney (Spears) n.

beer(s).

2000		Indep. Weekend Rev. 12 Aug. 4: When seeing that many ‘Britneys’ off / You get a technicolor cough.
2003		‘Alcohol’ Doctorjob.com 🌐 Britney Spears (beers) – ‘oh right, just four Britneys then, darlin’.
2005		P. Howard Curious Incident of the Dog in the Nightdress 81: I just tell him to [...] get the Britneys in.
2015		N. Cummins Tales of the Honey Badger [ebook] [They] are generally inclined to head out for a couple of Britney Spears.