Green’s Dictionary of Slang

1. (US campus) a gullible person.

1989		P. Munro Sl. U.
1995		L. Stavsky et al. A2Z 7/2: biscuit – sucker: He play me like a biscuit.

2. (US) a weakling, a coward [euph. for bitch n.¹ (3a)].

1998		D. Senna From Caucasia, With Love (2000) 40: Go back to the jungle, darkie. Go wash your ass. Go, you little culahd biscuit.
2002		‘Touré’ Portable Promised Land (ms.) 64: Biscuit [...] a weak man who can be robbed easily.