Saw this one (or a similar one) IRL years ago. I also knew someone who showed an appalling inability to get it, and who was convinced it was a logic joke - since the premise is false, the if-then implication was true, regardless of the truth of the conclusion.
My answer is always that I drive just fast enough.
'How shall a man judge what to do in such times?' 'As he ever has judged,' said Aragorn. 'Good and ill have not changed since yesteryear; nor are they one thing among Elves and Dwarves, and another among Men. It is a man's part to discern them, as much in the Golden Wood as in his own house.'