I must admit I tried to improve my MPG by accidently putting in diesel. I had been driving the car for a long while, and the engine was hot. I filled up at a mom-and-pop gas station, and their pumps were not labeled. I picked the one that was cheaper (regular leaded, this was a while ago).

I then went to pick up my girlfriend in my dope ride, a 1966 Dodge Dart with a slant six engine. We started heading home, when the car started acting sluggish. It got worse, and it was smoking pretty badly. I turned around and headed back, since I didn't want to get caught in the Adirondack mountains in New York at night in the snow with a dead car.

I must admit, the car did not die on me. The plugs were hot enough to get the diesel ignited, especially since about a quarter of the tank was gasoline. We made it back, and I spent six hours draining a full gas tank into bottles. I found some guy with a diesel truck, and I donated it to him. He didn't mind the extra gas kick to the petrol.

After this incident, I found two things. First, just as suggested by mgriffithsuk, sniff the nozzle if you're unsure. Secondly, Sears Die Hard batteries lasted through over 100 start attempts. I was impressed.