I note the suggestion to use the fire extinguisher
Lets hope the security bods at various airports don't read this
And it really can be the people you least expect that give you the most grief.
The nearest I got to belting someone was with a 70 year old 65kg granny. I am 105kg big lad and she refused point blank to surrender control on a trial flight. Wouldn't respond to anything I said and when I prised her hands off the controls 2 secs latter they were back on and I couldn't over power her on my set. In the end on approach I took a knuckle down the front of her chest while pitching the nose high. When she let go to stop me I pulled the seat adjuster and the seat went to the back of the track and she couldn't reach anything and I had to avoid her arms battering around as she struggled to try and get the seat forward again to be able to reach the controls. Landed and she never said another word and walked straight from the aircraft to her car without a backward glance.
Scuffles in the cockpit are bloody scary for any level of experience of pilot.