When you factor in how many passengers I can carry on my SUV vs. on my PCars, my SUV is way more efficient...
I had this debate with a witch at WDW's parking lot. She parked her SL600 way too close to my SUV (she parked after me) and I was not able to open the door to get my kids without getting to close for comfort to her door.
I politely asked her to scoot over a bit and she launched on this rant about large cars and fuel economy. She ticked me off to the point that I pulled out a car magazine I had on my truck and showed her the MPG ratings of her car vs my monstrousity....
I also took advantage and complained about her cigarette and her friends cigar smoke and its effect on the environment (hey they started it all

).
I made my point that day! When we came back, we had 2 flats.... Which got reported to the police and WDW had video of it. Priceless
Now that is funny!