You might share everything from tattoos to clothing to your inner-most thoughts, but there is probably a secret or two you're not sharing with your BFF. Maybe the truth would hurt their feelings. Maybe it would ruin their trust in you. Or maybe you've committed a felony and don't want them involved for their own good. Awww. Whatever the reason, some things you have to keep to yourself in the interest of preserving the friendship.
1.) From Grandmere13:
I never told my friend that I know that her and her boyfriend used to steal food from my house.
Her boyfriend at the time basically stole from everyone and was always getting fired from work for stealing from the till.
The bit that upsets me is that she knew full well that if she needed food, I'd have given it to her. She didn't need to steal the stuff.
She ditched that boyfriend which is why we're still friends. (And she doesn't steal from me anymore.)