Green’s Dictionary of Slang

1. (US black/teen) to ruin, to undermine; usu. as crumb a/the deal.

1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 26/1: CRUMB THE DEAL. Spoil a plan; as when a crook complained that either a confederate gave away, or the cops discovered, a criminal plot.
1930		R.E. Howard ‘Sailors’ Grudge’ Fight Stories Mar. 🌐 I can see where you crumb the deal some way and if it looks like we’re friends, I’ll lose my job!
1950		Goldin et al. DAUL 53/2: Crumb a deal. To bungle a plan.
1962		P. Crump Burn, Killer, Burn! 292: I’ll be damned if I’m going to smarten him [...] and crumb this deal.

2. (US) to malign someone.

1965

J. Thompson Texas by the Tail (1994) 190: Don’t crumb me with him, please! Don’t knock me, for God’s sake.

3. (US campus) to feel sad or depressed.

1989		Eble Campus Sl. Mar. 2: crumb – feel sad or depressed [...] ‘She was crumbing over that exam she failed’.
1996		Eble in Sl. and Sociability.