It is TOTALLY a stupid question, because OBVIOUSLY you should drive. It is based on the false premise that there is actually a choice. If somebody were to sincerely ask me this question, actually believing that walking was an option, I'm not sure I could resist the temptation to say "walk", just to see what happens next.

Only slightly evil, because the worst-case consequences are an unnecessary 100m walk. I think I could get that past an ethics committee, if I wanted to run an experiment to see what percentage of human responders would ACTUALLY walk to the car wash.