How do you act like you dont care for a person?

In order to act like you don't care, you have to make sure that nothing boy/girl says or does gets to you. Pretend to focus on something else and make it look like it's 100 times more interesting that whatever they're doing. Put in headphones if it helps. If you make eye contact, roll your eyes and make them think they're being really immature. But remember, don't be overly harsh because chances are if they're teasing you, they are seeking your attention and just don't know the proper way to do it.

Just remember not to react harshly to anything they do, because that will give them the satisfaction that they want.