Arm all crew with guns. Teach them to shoot to kill. Paint yellow line on floor aft of cockpit. Remove dangerous lockable door.
During welcome aboard PA advise that anyone who crosses the yellow line will be shot. During induction advise crew ditto if they act irrationally....or serve cold coffee.....or do a bad landing.
Israelis may be willing to share how they stopped all this hijack crap, but I bet they don’t agonise over switches being bumped or 60kg Flight Attendants going berserk. FFS.
That armoured lockable door is the real threat, as we have seen on several suicide flights and at least one where pilots were incapacitated.