"Insults" could be a very long thread. Seeing how much this Board produced in the "as cold as" thread, I imagine we could come up with at least a dozen top-notch zingers in each of these categories:
as cheap as ... [Tighter than a gnat's ass. If he had flu he wouldn't give you a sneeze.]
as ugly as ... [a mud fence. You look like a professional blind date.]
as dumb as ... [You couldn't find your rear end if it was on fire] A huge category
as useless as ... [tits on a boar hog]
as immoral as ... [loose as a buck of soot]
as angry as ...
as nasty as ... [a two-stingered wasp] [meaner than turkey-turd beer]
as stubborn as ... [so stubborn they call him old iron-ass]
as poor as ...
as old as ... [He's older than dirt. He was a waiter at the Last Supper]
as messy as ... [look like you were chawin' tecabby and spit upwind. like you threw your clothes in the air and ran under them.]
as drunk as ...
as crooked as ... [a dog's hind leg. So crooked he could hide behind a corkscrew]
as dishonorable as ... [so low you have to look up to see hell. lower than a snake's belly.]
as brassy as ... [She has more nerve than a toothache.]
as talkative as ... [Your tongue wags at both ends. She speaks at 140 words per minute, with gusts up to 160]

not to mention the various insults to body-size and shape.

Source: The above insults are culled from a collection of regionalisms, Like we Say Back Home by Dick Syatt.