What would happen if someone put diesel fuel in a gasoline powered car?

Well that would depend on how much... Friend put about 4-5 gallons in a pickup with a 31 gallon tank; diesel doesnt ignite from spark plugs like a gasoline engine does, so it will bog down and die fairly quickly... If it was only a small amount, top off the tank with fresh gasoline, and try to crank it. Most likely though, the diesel will be in the fuel lines, and you have to unhook the fuel inlet line and bleed out the diesel for a minute and then hook line back up and it should start. Add some fuel injector cleaner to the tank as well, and keep the tank topped off with gas for a few weeks and the gas SHOULD dissipate the diesel which essentially is fuel oil. If you FILLED THE TANK, however, you'll probably have to drain it completely via a pump or something and then bleed lines and such. Question is, how the &"$% did you fit the diesel nozzle in your gasser?