In up the Duff?

'Up the duff' is a euphemism for pregnant. It is used most commonly, although not exclusively, to describe unplanned pregnancy.

What is the origin of the saying up the duff?

The OED has it from 1941 and originally Australian. They say: Origin uncertain; perhaps related to duff n. 1 b, and hence analogous to similar slang phrases for pregnancy such as in the (pudding) club or to have a bun in the oven.

What does Duff mean slang?

Standing for designated ugly fat friend, duff is a rude, though often humorous term people use for that one friend who makes you look better.