Privacy at stake

I went out with Matt and his coursemate the other day for a steamboat. They were laughing at some of their friend because I did not approve them as friends in Facebook. The only thing I don't understand is why should I add them as friend when I barely know them? My Facebook is my own private platform and I don't mind if people say that I am snobbish. I even ignore friend request from my secondary schoolmates because I consider them as acquaintances and not friend. So, say whatever you wanna say about me because I'm only concern about my privacy...........