fisherman's dozen 

Unlike a baker's dozen, which is 13, the fisherman's tendency to boast and lie means the fisherman's dozen is 9 fish.

Similarly, the fisherman's foot is a fish that isn't really a foot long, even after the fisherman steps on it.

"Yo, Cyrus, how'd you do out there? You fool any big ones?"

"Eh, not bad, Lem. I caught a dozen, and four of 'em were over a foot long!"

"Tell me, lad, do you mean a fisherman's dozen, and a fisherman's foot long?"

"You saw right through me, Lem, but they'll fry up nice."

fisherman's dozen by Oliver Faltz December 23, 2011