The best thing to do is ignore the dude, but if he gets to close, tell him simply if you don’t back the guck up I will fuck you up. That will most likely scare them off. If that doesn’t work, simply fuck then up, it’s not like they’ll call the police. If he’s a punk, a good shot to the face will take him down, or a swift kick to the balls. I prefer both, starting with a kick to the nut, a punch right in the eye, works all the time