I know!.. but yeah.. Really!
some definitions of smartass go like this :
1. someone who makes wisecracks and acts cocky (idioms.freedictionary.com)
2. One who is particularly insolent, who to tends to make snide remarks or jokes (en.wiktionary.org/wiki)
3. Someone who is always trying to seem more clever than other people in a way that is annoying. (dictionary.cambridge.com)
.. and on top of it all, there's a scene in the first season of a TV series called "Breaking Bad" that in it, the main role uses the word (smartass) in a situation that corresponds to the meaning in question. as a side note, he uses the word to address his son, so I guess the meaning isn't that bad!