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.
"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."
someone who mouths of to provoke or be funny to people/persons.
usualy ends with the smartarse getting a severe beating :P
guy 2: i dunno, i have to get my animal book to find out.
both guy 1 & 2 are being a smartarse.