If the person has got extreme cool teeth when she is smiling, or got a face that automatically says to you "that gotta be a sweet little beaver!" BBF is your best friend for life!
!!! - You don't use this word if your friend is not sweet=)
'Best Behaviour Friend'. A friend or acquaintance in your socialcircle, whom you for one reason or another feel that you should be at your best behaviour around.
"My BBF came to the party, so I had to restrain myself hugely. If he hadn't been there, I'd have drunk so much more, and ended up dancing naked on the tables as I normally do when I've donetequila slammers"