"Lower than a snake's belly in August." -- No idea why it has to be August, but there it is. Something to do with trying to get "lower" than the heat for a creature that's already low to the ground anyway?
"Mad as a wet hen." -- A favorite of my mother. Presumably, moistened barnyard fowl are prone to particularly excessive rage.
"Blitzed," "schnockered," "p*ssed," "three sheets to the wind," "inundated," "high as Georgia pine," "liquored," "hammered," and "walloped" -- All euphemisms for a state of inebriation.
"Stun-gun stupid." -- Used as an adjective, more to describe an individual than a circumstance. One of my favorites.
"Fell out of the ugly tree and hit every branch on the way down." -- Unkind description of someone's comeliness, or rather, lack thereof.
"You can take as long as you want in a gunfight, as long as you're the first to draw." -- Cowboy wisdom used to denote a situation where an ultimate decision rests with a particular individual and must come sooner rather than later. Somewhat akin to "Fish or cut bait," which has been previously mentioned in the thread.
"Slow as Christmas." -- Presumably because, for some, the arrival of Christmas (or other appropriate holiday that involves the giving, or more to the point, the receiving of gifts) cannot happen soon enough.
"Slow as molasses in winter." -- Usually aimed at individuals or actions, not necessarily events or circumstances.
"Mean as a rattler and half as cuddly." -- Illustrates the particular degree of orneriness possessed by some.
"Burning daylight." -- I've heard people use this one, and don't know if they got it from the John Wayne movie
The Cowboys where the very words are spoken by the Duke, or whether the writers of that film heard it from others and incorporated it into the script. Either way, it means "wasting time."
"Hurts like the dickens." -- Another of my mother's favorites, often said after striking thumb with hammer accidentally, or similar painful experience. Mom and Dad don't cuss much.
On the other hand, I, and many of the other folks I know (including siblings), do:
"Slimier than two eels ******* in a bucket of snot." -- Where ******* is a gerund sometimes used to denote the act of procreation (or recreation).
Warrior Poet