When I was a teenager we had a 1985 300TD wagon. Living in NJ, everything is pumped for you. Stupidly, my sister and I went to a gas station (no diesel there) and they guy pumped regular gas into it and we drove it home.
The Wagon quickly started to make funny noises. We were close to home and realized what had happened. I don't know how much it cost my dad but I know I will NEVER make that mistake ever again.
We have the X5D now and always scope out diesel prices. Our other vehicle is a pick up truck (gas) which I think we have driven a total of .5 miles just to deal with alternate side of the parking so we don't have to worry much about forgetting which vehicle we are driving.