I've never gotten to sit in an owner's car, but pretty much all the car owners I've met have been nice/cool. In fact, I can't recall ever meeting a mean owner of a supercar.
The closest I've come to that is when I saw
this Vanquish. After taking about 4 photos, a guy came out of the car next to it, wagging his finger and saying to stop. He said it was his client's car.
Another time, I was taking a quick photo of a Datsun 810 wagon I found in a parking lot. A lady (the owner) walked up to me, saying that she noticed me taking a photo. I was like "yeah, (etc.)" and then I noticed she looked kinda pissed. I told her that I could shop out the plate, and she was like "uh yeah, you better do that".
And of course I've gotten told various times at dealers not to take photos or to delete any I've taken.