Green’s Dictionary of Slang

(drugs) a very small marijuana cigarette.

1985		‘Jennifer Blowdryer’ Modern English 79: skinny joints (n): New York PInner [...] Toothpick.
1992		Bentley & Corbett Prison Sl. 75: Pinroll also Pinrolled Joint and Pinner Used to indicate the small size of a marijuana cigarette.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Pinner: A marijuana cigarette the size of a toothpick.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 141/1: pinner n. a very meagre marijuana cigarette.