WATCH: Kirstie Alley's Revenge!

It was all fun and games for David Letterman all those times he was cracking jokes about Kirstie Alley's weight on 'Late Show' (Weeknights, 11:35PM ET on CBS). Remember this one?

"Kirstie Alley joining 'Dancing With the Stars.' If you don't already own one, now might be a good time to get a wide screen TV."

Kirstie Alley does, and she brought notes of several of his cracks at her expense for her appearance on his show.

Letterman said he felt he had her implied approval, since she'd said "it's okay" about them on an earlier appearance. "I said it's okay, so that was like go ahead and tell 50 of them?" she asked.

He really had no come back for this, though he tried. "We do love you and if you were skinny we would tell jokes about you-- No, probably not."

Even if this exchange was in jest, and it surely was at least on some level, it does raise an interesting question about why weight joke are so acceptable in a society that's so sensitive about jokes that single out any other specific groups of people.