You're on a flight when you witness

a man giving a female flight attendant a hard time about buckling his seat belt, refusing to do so with the seat belt sign on due to turbulence. The argument escalates when the man stands and tells the female attendant to get out of his face or he's going to knock her out. She leaves and enters the cabin apparently to talk with the pilot/co/navigator about the problem. The agitated male sits back down.

She reappears with what looks like the Capt. walking down toward where the agitated male is sitting. The seats directly behind his row have been vacated by passengers attempting to move away from a potential problem as it's apparently he's having a melt down of some kind.

You're 5 rows behind all this goings on, witness the above.

What would you do, if anything. What could you do if you were to intervene in some way before or after it escalates to violence with the capt.