chuff

15th century, dialectal, from Middle English chuffe (“a rustic, boor”), in noun sense “stupid fellow”. Adjective sense “surly, displeased” from 1832.

Onomatopoeic. Compare chug and puff.

1520s, in sense “swollen with fat”; circa 1860, British dialect, in sense “pleased”. Possibly related to “coarse, stupid, fat-headed” sense (see etymology 1 above). Or, perhaps a euphemistic alteration of fuck or another expletive.