Green’s Dictionary of Slang

1. (US black) raw, unadorned.

2007

B. Coleman Check the Technique 270: ‘I love that album. How raw it was, how grimy it was [...] the way I felt living in the ’hood’.

2. (US campus) wrong, unsatisfactory.

2008		‘Grandmaster Flash’ Adventures 171: penny: ‘I’m talking about that grimy stuff.’ [...] I know how you're smoking that base’.
2014		C. Eble UNC-CH Campus Sl. Spring 2014 7: GRIMY — not right.

3. (UK black) term of approval, good, amusing.

2017

theculturetrip.com ‘Guide to London Slang 10 Jan. 🌐 Grimy – good, or may describe a practical joke or amusing act.