What to do if a user is threatening to hack the account of another user?

There was some internet drama going on about online relationships. It went overboard. Pretty sure there was some violation.

...made a mistake, she is going against me, well someone's gonna get hacked, Ha, tomorrow her account will be no more.

...I'm already hacking her, I'll read her messages.

It's probably just acting tough, but do I report this?