From a friend of many years ago, with a rural upbringing:

Upon observing a female hitchiker: "Don't stop! She's uglier than Death taking a shit!"

Of his wife, when he disagreed with her on some point or other: "She's crazier than a shithouse rat!"

One of my favorites from a list the late H. Allen Smith put out in one of his jokebooks:

"That woman was so tall she could stand flat-footed and piss in the radiator of a Chevy pickup." (You have to be old enough to remember outside radiator caps on cars and light trucks, for that to make sense.)

Peter.