The reason she seems so snappy when I say something?

This has to do with a friend that I have and a girl that I'm not much friends with but we're sort of cool. When I say certain things to them they get serious attitudes about it and I'm not really sure why. It's never anyone else, just these two. It's never anything about them either. For example I can say "Those Black Sabbath concert tickets cost $200. That's too much even for Black Sabbath. You ever see them live before" and both of them will respond to me with something along the lines of "No I didn't see them live but I know who they are. Why are you acting like I don't know them? Like I didn't hear them before?" They do this with everything all the time and I just want to know what's the deal? They don't only do this to me, they do this to a lot of people. If you say or ask something about a certain subject they get angry because they think that you think they don't know anything about that subject or that you're trying to insult them.