best friend for the win; the kind of friend you can depend on for anything and will help you whenever you have a problem
There is an old saying that says a good friend will come bail you out of jail, but a best friend will sit with you in jail for the night. Well a BFFTW will break you out of jail using a helicopter, just so the two of you can go to a movie together.
Because Fuck You, That's Why. A simple and clean reason to do anything without any reasons provided... or better yet, the reason is "Fuck you". This phrase is used widely in memes.