Originally Posted by chaymus
It's a difficult problem, they're purposefully trying to elevate themselves by bringing you down, and the kicker is if they get a rise out of you, you're less mature. I would avoid losing your temper and as politely as you can ask them why they feel the need to do so.
It could be the person is immature, or the people around them are jerks, or some combination of the two. Without a few details - the more the better - it is hard to tell which is which.