That smart arse was just trying to look good in front of the boss.

那个自作聪明的家伙只是想在老板面前表现得好一点。

A smart arse is more common here in Australia and I think that smart aleck is more common in the UK.

Smart arse 的这种说法在澳大利亚很常见，而 smart aleck 在英国更常见。