The funny thing about that joke is how Americans can never get used to the speeds on German motorways. 150 km/h is nothing. (And no, I don't think it's great. We need a speed limit ASAP.)
Still, it was funny when I was driving that American guy around in Germany many years ago. He desperately wanted to try driving a bit himself on the Autobahn - no speed limit - woohoo - and then he chickened out at 130 km/h.