Hmm.
Interesting thread. I'd offer a number of points, since I've been in a similar situation before (reject of a new car due to failure of the cars gearbox within 100 miles).
Similar in that I wasn't happy. Not similar in that the dealer and I had a stand up argument in the middle of the dealership with me refusing to accept the car. Not good and not clever (for either of us).
I ended up apologising for my tone and temper, and suggested that we had another chat the following day, when we both had calmed down. I also asked if they would mind lending me a car until the following day - with me paying insurance / petrol. For context - we are talking about a 38k car here. Paid cash.
I expected the dealer to at least accept that I'd recognised my attitude wasn't helping - neither was his, and that calming down on both sides would be a good idea.
To his credit he did, offered me a car of my choosing, and we spoke the following day. To this day I still use the same dealer, and I've never had a problem - they are superb.
Thats a good story. Both sides learnt, and both sides had a good outcome. I've recommended his garage to a number of friends now, and all have been treated very well. Dealer quite often lets me drive newer models (some 100k +) just to have a go - recognises that at some point I may buy one (hoho).
On the bad side - I had a bad experience with another dealer. This time I didn't loose my temper, I just calmly asked to speak with the service manager etc etc. Nothing happened. I called the mobilo life people who are normally superb. They also tried - and nothing happened. One letter to MD UK, I had 3 calls back, and the problem was resolved immediately, with apologies all round.
So two different stories - two different approaches. Stay calm, don't loose it. I recognise you haven't - good. Write the letter to the MD UK, he has a special dept which deal with this kind of experience.
Final footnote - the dealer in the 2nd story is no longer.