One of the most important things to remember when facing a child that is experimenting with pushing your buttons by using sarcasm, is that the behavior needs power to continue. Therefore, do not give it more power. If you are faced with a sarcastic remark from your child turn to them and say, "Please don't speak to me that way. I don't like it." And then leave the room. When you leave the room you take the power of the situation with you. There is no one there for them to continue to taunt.
With older children you could try putting them on the spot by responding with a question such as, "Why do you use sarcasm when I ask you about ___________?" If they deny being smart with you, remember to take the power back and simply say, "Alright. Let's refocus on what we were doing. And please remember, I do not like it when you use speak sarcastically." And move on. Do not rehash it no matter how tempting it may be and how frustrated you are. Remove the fuel from the fire and move on.
If you feel that your child is going beyond simple sarcasm and could possibly be crossing over into verbally abusive behavior, please contact a professional for help. Behavior that is harmful to themselves or someone else is best dealt with by a professional. There are many Christian counselors out there that are trained to help families deal with this issue. If you are unsure if the behavior is abusive, do some research. I've posted a link for an article below that could help define the boundaries.
http://www.empoweringparents.com/Child-Verbal-Abuse-and-Threats.php?&key=Abusive-And-Violent-Behavior
http://www.empoweringparents.com/Child-Verbal-Abuse-and-Threats.php?&key=Abusive-And-Violent-Behavior
