A person who, by means of purpsose or not, uses sarcasm to have a laugh. A person who, on a regular bases, annoys the hell out of people with their sarcastic-attitude.

Someone who enjoys giving flippant, sarcastic and/or rude answers to legitimate questions; also someone who enjoys being sarcastic and rude in general. See also: wise-ass, smart-aleck, etc.

A mule/donkey of unusual intelligence

A person who just has to make everything make sense. Speaking of which, smartass is a oxymoron because an ass is a stupid person so smartass means "smart stupid person".
(not exactly the opposite of dumbass because a dumbass really is an idiot but a smartass isnt neccessarily a genius)

a person who persistanly uses sarcasm as a means of communication.

An annoying asshole who attempts to use sarcasm every chance that he/she gets.

N. A person who indiligently tries to provoke your thoughts, concerns, ideas, and opinions by arguing and becoming outspoken on their own part.

N. A very outspoken person

Adj. A word describing someone under a description of a smartass