One of the biggest parts of maturity is properly dealing with our anger. If you have a problem with someone you need to confront them about it, and not going around being a jerk, ignoring them and doing immature things towards them such as switching seats just so you don’t have to deal with the issue. I don’t care if you have a problem with me, but at least have the decency to act like an adult about the situation, when you are eighteen years old you need to realize you need to grow up.
If you become anger with someone, do not going and pout or do things as “pay back”, trying to hurt them. Calmly tell them why you are angry and figure out how to move on from them. You have to deal with the problem sometime especially if you are going to see them very often in the next few years.