I think this is a rather difficult task. You can tell your bf/gf that the relationship is over, but how do you tell a friend that you dont want to be friends anymore. I've had occasions when some friends call to go out for a drink/makan/yumcha whatever, in which I would politely decline but they still call you. It makes me feel guilty, and it's not really their fault or my fault. There's various reasons why friendships fall out
a) Friends drift apart - different lifestyles and thinking can be a major factor.
b) People change- that's inevitable. And sometimes friends change to something you dislike. Tell me how you can spend time with someone you already dislike.
c) Needy friends. Really, I dont mind to be a shoulder to cry on, a friend to rely on, blah blah blah, but if it gets too frequent, when the friend is constantly in need of attention, it gets pretty annoying.
d) Some friendships are somewhat obligatory. Childhood friends especially. When you meet only during birthdays/weddings- I really don't see a point.
I always believe life is short. Focus your energy on friends that matter and friends that is really in need of you. Friends made because they just wanna hangout with you, have fun with you, well it'll never last. Listen to : You've Got A Friend by Carole King