BBF stands for Bestest Best Friend. It is a special term used only to describe those whom you trust with your every secret and private thoughts. To become awarded the title BBF is to completely earn the trust of giver of that title. BBF's are inherently perfect. Those titled BBF's can have no flaws.
"I'm so stressed for mid-terms! I should call out my BBF!"
"I was so smashed last night, I would have been unable to go home if it weren't for my BBF!"
"Fuck man, why can't everyone in the world be as good looking as my BBF?"