I'd argue that the "can't get out of the car" thing is a parking joke, not a fat joke. I didn't get a sense that her awkwardness in climbing out of her window, then into the window of the car next to her was supposed to be related to her being fat, but just that it's really hard and annoying to do for ANYBODY. It's definitely slapstick-like physical comedy, but I don't think it would have been filmed differently if Sandra Bullock was the subject of the scene. Her door barely opens two inches -- even Twiggy wouldn't have been able to get out of that car.

Would it have PLAYED differently, or been received differently if the person climbing out of the window wasn't fat? I don't know. I think I would have enjoyed it the same, but I can't speak for any other audience.