What about writing out some devastating things that you'd hate to hear him say, then write out responses that you feel can validate without agreeing without debating?
Call me old fashioned. I work in the sales industry and I don't just show up to appointments and "wing it". If you think when you're full of adrenaline, your brain is skipping because it's going so fast, your heart is pounding, and you're having trouble breathing suddenly words of pure affirmation will magically bubble out of you as if you were a different person...well, I'd be a bit surprised. I believe that we don't rise to the level of our hopes, we fall to the level of our preparation.
Personally I would write out the 3-5 things you most fear hearing, plan responses, and practice them in the mirror. Then I'd have another 3 canned responses for stuff you didn't anticipate, more generic.
It will make you feel more confident to have a quiver full of arrows to fire back
This is awesome advice. When I find myself anxious about a meeting or event, it's usually mostly that I feel unprepared. PREPARE, and the anxiety level goes WAY down. And more importantly, the preparation will lead to you handling the various comments much, much better.