The dusty woman
In 'The Cook', while taking an order, Buster notices some dust/powder on a woman's back and neck. To her annoyance he starts to dust her off. Am I reading too much into this.. but I think I know what that joke meant. Possibly :P
I've seen a similar joke elsewhere, but I can't think where. But it generally seems to mean that if a woman has dust on her she's er.. been on the shelf a long time?
If that is what was meant, that's quite a risque joke!