Is it possible to get hacked on facebook?

I would say YES.
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Facebook passwords are usually gathered from keylogging, from you entering your password into a fake facebook site (phishing), java exploits from clicking links sent by an attacker, or from hijacking cookies via your wifi. Proper security practices will prevent all of these. The person threatening you is either buffing or a script kiddie.

He's obviously a script kiddie. If he could do it out of thin air he would have hacked your account already instead of threatening you.

Its very easy to get "hacked", most likely through your email. If you know basic information about anyone you can answer security questions and bypass and reset the password. Facebook gives you almost every single security question answer that most sites use as a generic question. Once you have the email you have every single account that is made through the email by "I forgot my password" method on websites you have an account on.

This is one of the many reasons why I disapprove of Facebook and don't use it at all.

Most likely he isn't truly hacking you but using your public information, along with your friends, that you guys throw out through Facebook that only your friend could see.

It's possible. That's why they have a "Bug Bounty" program, so that people disclose vulnerabilities and don't use them to destroy.

https://www.facebook.com/whitehat

But like everyone said above, the chances aren't that high, especially if your boy is just talking trash. Phishing scams are easier to carry out.