I'm like, super low-maintenance
Nobody's true personallity is that of a sarcastic asshole. You choose to be that way. Just like you can choose to say something nice instead of insulting someone. The reason sarcasm comes so easily and is your first response is because that's what you've been practicing so you're good at it. But if you would, as the guy above said, stop and think before you say something rude, eventually you'll start being a nice guy.
Also, being nice does not mean being a pushover.