Green’s Dictionary of Slang

used to accentuate one’s rejection of a statement or idea, e.g. do I thump! is she thump! etc.

1905		Marvel III:60 3: Is he? Thump! Honest you call him. Haw, haw, haw!
1966		M. Rumaker Exit 3 and Other Stories 142: ‘Rev, you talk like a disappointed man.’ ‘Thump! down the chute.’.
2013		K. Sampson Killing Pool 274: And what of Manners? Will he sit and wait? Will he thump!