Why do certain people act different around other people?

Ever since high school started, I noticed some of the people I thought were my really good friends are acting different when other people are around.

Lots of people change the way they act depending on who is around. But it sounds to me like what you are saying is that they might seem like they have your back, but when some other people show up its a different story. Welcome to high school. Anyone who has been through it can relate to what you are saying. My advice would be to bring it up next time it bothers you (maybe after the other people have left). Don't be a jerk about it, but make your point that you won't put up with it. Be the bigger man, and don't ever cut a friend down to gain points with anyone. Life after high school will be much simpler, at least when it comes to these kind of things.

i dont no y im putting an answer because I dont no if I no but I feel like I kinda do though. my cuzin do dis all the time when her crush cum around......she be actin like she all tough or what not. its not even cute,but hey.