Green’s Dictionary of Slang

1. a crossbred horse.

1859		Bell’s Life in Tasmania 16 Aug. 3/3: [of racehorses] [H]alf-bred animals, which it would be heresy hereafter to denominate ‘cocktails’.
1876		‘Some Road Slang Terms’ in Malet Annals of the Road 389: 1. Of Horses Cocktails...Crossbred ones.

2. (US drugs) the very last portion of a cannabis cigarette placed on the end of a cigarette.

1958		E. Gilbert Vice Trap 40: She clipped the holder to the cocktail and touched her lighter to it.
1969		R.R. Lingeman Drugs from A to Z (1970).
1977		(con. 1960s) D. Goines Black Gangster (1991) 242: Racehorse removed the burned-up joint from his mouth and made a cocktail.
2001		ONDCP Street Terms 6: Cocktail — [...] partially smoked marijuana cigarette inserted in regular cigarette.

3. (drugs) a cigarette laced with cocaine or crack; also attrib.

1992		V. Headley Yardie 129: D. built himself a cocktail spliff.
1997		C. Newland Scholar 156: Clarence built weed spliffs. Levi produced a gleaming crack rock from his pocket, making the trio yell and touch fists happily, all of them asking to build cocktails.
2001		ONDCP Street Terms 6: Cocktail — Cigarette laced with cocaine or crack.