If you accidentally just put a little bit of diesel in your tank, then you might be okay.
The same with very little gas in a diesel engine. Your gas car will just smoke a little and wont run the best until you burn it out. Keep in mind that I'm talking about less than a gallon for a full tank.
Different firing on the plugs, different plugs, different fuel system, different pressure, different fuel pump, filters, and injectors. Different everything between diesel and unleaded fuel engines.
ONLY if you like to walk ... it'll mess your car up!!! I cleaned out my engine after it had sat for three years with Diesel IN THE OIL, but you don't want to run diesel thru the fuel system, it contains oil. That just screws things up .