My generation is troubled

I plan on keeping this short just for my own health; why keep harping on something I can't change?

So just ten minutes ago I was walking home from class and as it is a nice day out, 3 guys were playing catch with a baseball. I asked if I went and got my glove if I could join them. They flat out said no and then laughed to themselves.
I don't understand why people must act this way. It is rude, unkind, and just makes me feel like shit. I notice mostly it is the people of my generation, teenagers, who have this problem with kindness.
People need a lesson in common courtesy.