From the Onion, the motherlode of dreadful similes. It's a joke, albeit rather thin.
Nonetheless, a sampling:
I've been told my diction's clear as strychnine.
I'm as hopeless as a springtime frog-fryer.
To tell it plain, my similes are confusing as the day is wrong, as disappointing as two peas in a pigsty, and more obscure than Kenneth from marketing (the guy who's as big as a thing that's six-feet-tall and 200 pounds).