>L1: Let's escape.
>L2: How?
>L1: I'll shine this flashlight up at the skylight and you climb up the beam.
>L2: You think I'm stupid? You'll turn it off when I'm half-way up

Ah, childhood memories. I figure I was six or seven when I heard them.

And, IMO, the best lunatic joke in my arsenal:

A lunatic walks down the asylum yard, pulling a toothbrush on a leash. Doctor walks by:

D: Um... is it you taking your dog for a walk?

L: You think I'm nuts? Don't you see it's a toothbrush?

Doctor goes away. When he's far enough, the guy addresses his toothbrush:

- Gee, Fido, we fooled him!

The older and weaker predecessor to this:

D: why are you pulling that toothbrush on a string?

L: pushing didn't work.