The administrator for the Good Clean Fun list was trolling rec.humor.funny...
Me: I'd like a pint of the jello salad, please.
(The kid behind the counter reaches for the cup-sized container.)
Me: Sorry -- pint, not cup.
Kid: Huh?
Me: (pointing) This size.
Kid: Oh. That's a pound.
Me: That depends on what you put in it.
Kid: Huh?
Me: "Pint" is volume, not weight. What that amount weighs depends on what you put in it.
Kid: This is a pound, not a pint.
Me: If you fill it with potato salad it's probably more than a pound; if you fill it with that marshmallow fluff it's a lot less.
Kid: Huh?
Me: Never mind, just give me a pound of jello.
In case you're wondering, my pound of jello weighed about 12 ounces.