On Sunday evening, I finally remembered to tell the "chocolate milk!" joke:
There are two penguins on an ice floe, drifting north into warmer waters. These penguins are very fond of each other, but they don't speak English very well. Suddenly, with a terrific crack, the ice floe splits in half, right between the penguins. As they begin drifting apart, one penguin sadly waves a flipper and calls out, "Chocolate milk!"
It's been a long time since I've told it in person; I had forgotten how disconcerting it is to finish the joke and have a room full of people look at you blankly.
It's a joke that gets funnier over time. The first time people hear it, most of them will look at you blankly. But then (if I remember right; it's been a while since I've done this) if you tell it to a mixed group of people who've heard it and people who haven't, the ones who've heard it before will sort of smile to themselves. And the next time they hear it, they might laugh a little, struck by the absurdity of the joke and by the blank stares of the people who haven't heard it before.
Eventually, it passes into folklore, and people start using "chocolate milk!" as a phrase of fond farewell.
I meant to tell this joke to Jay's extraordinarily charming five-(and-a-half-)year-old daughter Bronwyn, who might've been the right age to laugh at it even the first time (and, incidentally, who appears to be able to levitate), but I forgot.