The British or Commonwealth English
counterpart of the American English
" (probably the form in which it was invented, before being borrowed back into British English).
Calling someone a smart arse is intended to pull them down a peg or two for adopting a position of superiority, especially intellectual:
(1) through sarcasm
(2) by using obscure knowledge to score points off other people, or
(3) just being too f**king smug
when they're right about something.
"Oh, Alice, you're such a smart ass."
"Actually, Bob, I would prefer to be insulted using the correct, British English pronunciation: 'smart arse'."
"But, Alice, I think you'll find 'arse' has been pronounced 'ass' since at least Shakespeare's time, and therefore far pre-dates the division of English into British and American variants."