“He’s nuttier than a squirrel turd” - an eccentric person, who may or may not also be legitimately crazy.
“Toad strangler” - a heavy downpour. Also, “raining like a cow pissin’ on a flat rock”.
“Runs like it’s got a warrant” - an older vehicle or machine that’s still (mostly) functional, at least until you’ve paid me for it
“Butter my ass and call me a biscuit” - used to acknowledge an unexpected turn of events. Can be good or bad.