That car runs like a scalded dog.
He was running like his feet were on fire and his ass was catching.
Busier than a one legged man at an ass kicking contest.
Useless as tits on a boar hog.
Not the sharpest knife in the drawer.
Not the brightest bulb in the box.
He's one fish shy of a full stringer / a few cards short of a full deck.
Dumb as a box of rocks / Dumb as a stump.
Colder than a witch's tittie in a brass bra.
Hotter than a firecracker.
He (does something) like old people fuck.
(A group or person did something so badly it) looked like monkeys fucking a football.
He could fuck up an anvil.
She was built like a brick shithouse.
Crazier than a shithouse rat.
Nuttier than Chinese chicken salad.
I am hung like a horse.