Shitty Friends

What do you do when someone you thought you were close to is just a shitty friend?

What do you do if you get on someone's case because you care about them, and instead of admitting there's a problem, they blow you off and talk about you behind your back in malice?

I personally think that's a shitty friend.

And if this person's mentality is, "I'm a big boy, let me screw up my own life", but yet they act like an overgrown child doing it just because you told them not to, which works adversely in the "I'm an adult now" argument, what the hell do you do?

So buddy, take your little red ball and go home.. I'm kicking you out of the sandbox anyway.