Green’s Dictionary of Slang

(US Und.) something worthless; an informer.

1950

Goldin et al. DAUL 154/1: Pea soup. (General underworld, and chiefly prisons in Northeastern industrial area) 1. Anything that is worthless or good for nothing. 2. Anyone disloyal to the underworld. ‘That flea is pea soup. Chill (ignore) him.’.