Easily the funniest gag I ever saw was just after Reagan bombed Lybia. France refused to allow our jets to use their airspace. The next night Carson suggested American tourists avoid french airspace. The french were rather aggravated and the french embassy issued a terse statement. The next night Carson had on a ""french tourism envoy". Shortly after the guy started speaking Carson hit him in the face with a pie. OMG!!!! My heart stopped. We've just gone to war with france!?! Turns out the guy was just an actor playing a part. Classic.
I remember him making a joke around the same time, to the effect that "So France wouldn't let us use their arispace... Gee, they didn't seem to mind back during WWII".
Also, one day at school I commented to a friend "Wouldn't it be funny if they found out that cancer was hereditary in laboratory rats?". That very week, Johnny said almost the exact same joke in his monologue. I wanted to sue...