Secret Service: Just one question, Mr President. Is your car diesel or petrol?
President Obama: Leave it alone, Secret Service!
Secret Service: Oh no no no no, this is just curiosity, Mr President. Diesel or -
President Obama: It's petrol, it's petrol!
Secret Service: Right. So it's not diesel?
President Obama: No, it's not diesel.
Secret Service: Right. So it'd do a terrible amount of damage if I put diesel in?
President Obama: Yes it would. It would completely ruin the car's engine.
Secret Service: Well, hahaha! I certainly won't be doing that, then! HAHAHAHAHAHA!
It's a surprising career change for Mrs Doyle, but then no less strange than that exploding milk-float, I suppose.