I'm probably in the minority here but if you feel the need to go back there you should already have called the police. Flight attendants are trained to deal with irate and abusive passengers and are given the phrases to use to calm them down. If these don't work, you may be viewed as a threat to the passenger and escalate the situation. Call the police, it's their job. Then go and tell the F/A that you called them and ask them to go to the galley until the passenger deplanes. You should not engage the irate passenger.