Well dude threatened you, jumped on your back, and continues to talk shit. Catch him somewhere not public and beat the ever living fuck out of him, like to the point he's not getting up without help, and go on about your business. If he trys to press charges or anything, good luck proving it, call a buddy and have a solid aliby...
For the record, i have had to deal with a similar situation 5 or 6 times in the last year. i've had issues out a few local bars, so have my friends lol. No ones been to jail yet.
That or you can call the cops, file a restraining order, press charges, call the cops every time he calls or confronts you, and have nothing to worry about. Thats about the only two ways that shit goes...