yes, off course. If they are not nice to you, they are not the right ppl you should be friends with. In our life, there are always that kind of ppl. But if you are nice to them, I bet most of them would be nice to you.
I agree with what you say.
Most of the people will be good to you, if you are good to them.
Sometimes they become mean because they want you or challenge you to become more responsible.
They want to see if how you'll handle that kind of situation.