Many of us have a fair amount of stress and unresolved issues in our lives so it's not hard to overreact when people say or do something we don't like. Although we may try hard to maintain peace and balance, sometimes we are caught off guard by the words or deeds of others. When people "push your buttons" you have choices in how you can react. If you respond from a place of defensiveness, you run the risk of saying something you may later regret.
I find it easier to take a step back and take a close look at the offending person or correspondence. I may even go through a series of breathing exercises or meditation--to get clarity on my feelings and thoughts. Usually, if I allow myself an "emotional time-out" before I respond, I am able to stop that catastrophic slip of the tongue and save myself future pain and embarrassment.
If someone is truly being hurtful or obnoxious, don't give them the satisfaction of lowering yourself to their level. Instead, respond with kindness, patience and love. Remember that words make a powerful impact and once harsh words are spoken, they cannot be retracted. Think before you speak (or write) as wounds inflicted by words of anger or hate can last a long time.