Someone where I work is always sarcastic and overbearing

do the exact same thing back, they wont be able to stand it. i've got a mate who is always making jokes at others expense, doesn't really bother me but really pisses some people off, anyway if you ever try to make fun of him he always gets really offended and defensive, its actually quite funny

like my mom always says "kill em with kindness" and dont act like it bothers you..I've found it really helps..

That sounds like you boss. I would just smile and pray about it seems like they can help it. It is always one bad seed in a apple. as long as you are during your work. dont worry about it. Don't let them indimidate you. are you in a union? if you have a problem with this person, file a grievence. document everything they do to you.

I would tell them when they are caustic and not deal with them

well, i would say be the same too...and maybe more. but it will really make your life unbearable and sad whenever that person is around. if im in your shoe, i will treat that person as invisible..that's the best way to go about it. when he/she is invisible, nothing they do/say will be able to get to you, right? life is too short to be bitter and angry over person like that. Offer him/her to the Lord...you know there's a reason why you have to be working with him/her.. :D

The only thing i can say is don't react. it will be hard but i'd get one of those stress balls and give it a good squeeze under the desk if that person was annoying me! lol!