Urbandictionary says:

smart ass 352 up, 43 down

Someone who is sacastic, in a cutting yet witty manner. A person capable of making a remark that could be interpreted as a insult or a joke depending on the sensitivity of the listener and the specific situation. A smart ass is not necessarily a bad person just usually perceptive. ( For terms to refer to an offensive, cruel and asinine person see Jerk, Asshole , idiot, fool etc.)