To me, this is central to the idea of being a friend. A friend is someone who's there for you, and unstinting and unwavering when you need help. I try hard not to let my friends down in that department. Most of the time, I even succeed.
I see no contradiction in others saying that I'm not kind and generous. There are folks out there - even some of them on LJ - who have managed to make an enemy of me. I'm not quite as bad as one fictional character who "held grudges until they died of old age and then had them stuffed and mounted", but once someone has gone to the extent of not just getting me mad at them, but truly making an enemy of me, I'm not inclined to forgive easily - or, absent exceptional conditions, at all.
I have no problem with the idea of being some folks' best friend and others' worst enemy. Those are not at all incompatible.