GearDownFlaps
My first ever flight as a FI was with just such a gentleman. He was in for a checkout and had stormed out the day prior when he found out he couldn't just pay and go off with an airplane. Older guy, experienced GA pilot, me the kid supposed to determine that he was safe. They gave him to me as a test I'm sure.....
Be 100% respectful and perhaps try to present it in a slightly different light, such as emphasise it as an area and airport familiarisation flight as much as an insurance checkout, so as to help 'em feel that they're not being 'examined'.
The toughest thing I found wasn't attitude problems, with established pilots it was trying to decide, as a new FI, where the lines were drawn on standards. This guy was outside standards a little on the manoeuvres but was safe and a good stick, procedures were a little different. Trying to drive me across the active runway without clearance was a problem
He was also unable to start the 172SP after haughtily dismissing my suggestion that we sit with the POH for a few minutes and familiarise ourselves with the vagaries of our particular aircraft. He'd not flown a fuel injected engine before and my point was well made (but not patronising) when he finally relented.
Debrief was toughest but you have to stick to your guns if there's something you need to talk about. By then hopefully they've warmed to you a little and understand the necessity, with this guy I simply had to insist on some ground ops to cover the near runway incursion. You'll hear a lot of excuses. Don't dismiss them, use them to suggest an alternative course of action.
In the end don't sign 'em off unless you're happy.
Oh, and clean the window!