Why do people always INSIST on making snarky comments?

What do I mean by this?

Someone will say something...

and there's always SOMEONE that HAS to say something rude, sarcastic, harsh, bitchy, etc.

But why?

What exactly is it that makes people decide, "You know what? I'm going to be an asshole & say something following up what he/she just said to hurt their feelings."  Why?!  I can't stand when people do that.  Whether they're doing it to me or not, it still always pisses me off.  What's the point in being an ass and saying something to make fun of what someone just said? What's the point in making fun of them?

I don't see it.  Honestly, I can't recall many times that I've done it to someone.  The only time I can think I've done it is because they said something rude, so I had to follow up with something rude to put them in their place.  But just doing it to someone for no apparent reason just because you're an asshole isn't right.  It pisses me off!  

It's like no matter what someone says, there's always going to be someone to throw in their damn two cents and be an ass.  I hate people. >_<