Green’s Dictionary of Slang

dirtbag adj.

[dirtbag n.]

repellent, disgusting, despicable.

[US]C. Hiaasen Tourist Season (1987) 20: ‘Tell me about Ernesto Cabal.’ ‘Dirtbag burglar.’.
[US]J. Wambaugh Golden Orange (1991) 50: Uses meth and other dirtbag drugs.
[US]J. Lerner You Got Nothing Coming 118: Dick-licking dirtbag Dirtboys!
[UK]Guardian CiF 10 Dec. [Internet] It’s the dirtbag left, who have had enough of privately-educated nonsense merchants wibbling on about progress.
Tablet 9 Jan. [Internet] It also doesn’t mean aping Trump’s demagoguery with a left-wing sheen, as dirtbag leftists would have it.