I walked up to his desk and said "Is that a race track out there ? I didn't know the speed limit was 100mph and did you realise it was raining blah blah".
He jumped up out of his seat and said "Look it's nowt to do with you I was test drving the car. Are you the Mercedes driver ? Anyway you were nowhere near the junction".
I said "I don't care how far away I was. If that's the way you drive normally then you are putting people's lives at risk and I may be not so far away from the junction next time".
He followed me out of the showroom and said several times "just get in your Mercedes".
If I was the dealer principal, he'd be in my office simply for speaking to a member of public in that tone, knowing that he is a representative of my company.
In any case, it's certainly not the right response (the way he responded) but I'd just let it go. Not worth the hassle.