stiff-assed; stiff-arsed adjective used of a person who behaves in a superior manner and doesn’t mix with others US,1937
But you’re one of those stiff-arsed moralists who see a favor as an opportunity to show their piss-green incorruptibility rather than their gratitude. — Peter Barnes, Laughter, 1978
Sure, and would ye rather I was mealy-mouthed like those stiff-assed ponces from London? — Chet Raymo, DorkofCork, p. 343, 1993