Just remembered - Jethro had to give Mr. Drysdale a ride and it was night time. Mr. Drysdale says "Jethro, aren't you going to turn your lights on?"
Jethro replies "why? Do you plan on doing some readin'?"
Sad to admit it, but there must be a lot of "Jethros" where I live because you can't drive more than a few miles from my house and not see a few people without their headlights on at night.