off-ox, n. — Green’s Dictionary of Slang

off-ox n.

[lit. the ‘offside’ ox of a pair, presumably linked to such characteristics]

(US) a stubborn or headstrong person.

1848		J.R. Lowell Biglow Papers (1880) 79: Ez to the answerin’ o’ questions, / I’m an of-ox at bein’ druv.
1903		DN II 352: off ox, n. One who is usually on the opposite side of a popular movement.
1915		M.G. Hayden ‘Terms Of Disparagement’ in DN IV:iii 209: off-ox, a cross-grained fellow. ‘My grandfather was always an off-ox’.