Green’s Dictionary of Slang

pus-bag n.

also bag of pus, pus brain, pushole, pus-nuts, puss-bag
[nuts n.2 (1); the use of SE pus may offer a link to earlier derog. terms relating to venereal diseases]

(US) a contemptible person (cf. pussbucket n.).

[US]Baker et al. CUSS 178: Puss bag Constantly complaining and irritable.
[US]S. King Stand (1990) 344: Why, here’s the wise-ass pusbag, what’s the story, pusbag, got anything smart to say? [Ibid.] 740: ‘Like it, dontcha?’ The Kid panted. ‘I knew you would, you bag of pus.’.
[US]S. King It (1987) 50: Along come these three pusholes in their engineer boots and they steal his life.
[US]S. Morgan Homeboy 252: I got your number, pusbag.
[US]R. Marcinko Rogue Warrior (1993) 211: Those sorry motherfucking cocksucking pencil-dicked shit-for-brains pus-nuts goatfucker assholes.
[US]J. Wambaugh Finnegan’s Week 248: ‘Here, pus brain,’ she said.
[UK]I. Welsh Filth 80: Two puss-bags known as Setterington and Gorman.