Green’s Dictionary of Slang

1. a thug, a gangster.

1972

Times 27 Jan. 16: Trotskyist, in Labour terminology, is virtually synonymous with hooligan, hoodlum, ruffian, droog.

2. (US campus/teen) a good friend.

1996

Eble Campus Sl. Sept.

3. a dull person.

1999

Guardian Rev. 17 Sept. 20: You’re one of the apathetic droogs responsible for the demise of these events.

4. (also droogie) a young man, esp. working class.

1999		Guardian Rev. 1 Oct. 16: When angry young droogs such as The Who and the Stones began lashing out at ‘the establishment’ in the 60s, working (and lower middle) class youth suddenly had a radical new voice.
1999		Indep. Rev. 2 Dec. 8: The word ‘droogie’ can be caught in his song ‘Suffragette City’.