Maui I have to agree with Gimbo on this one, though my reply will be to politely open the mixture/throttle up and have a discussion.
I am sure you are good at what you do as you do continue to do it everyday BUT one thing you must learn is that even though you are the "captain" you can and will learn from the person in the right seat (or left in this case). To assume you know better if often fool hearty and most likely dangerous. Alwya keep one ear and one eye open and you never know what you may pick up sometimes.
I have done this before and will continue to do it. That is both listen and on the odd occasion put my foot down. I will not accept an engine failre if I deem a situation to be dangerous and am more then willing to discuss in the air and/or on the ground and usually do prior to the flight. This draws the "safety line" in the sand and pretty much tells me what sought of person you will be to fly with in a "Check and Training" role.
Many people are set in the ways they conduct themselves on tests, and good bless his sole, have brought highly experienced people to their unfortunate deaths. As for destroying the aircraft, well lets just say you can do what you can do but when it hits the fan are you landing ahead..... or just further ahead? The 1% is not always the case as we all know... have you flown a Twin Comanche lately at ISA +25?