"Shaking like a dog shitting razor blades" is the opening of an alkaline trio song. They're out of Chicago, so I don't think this is local to small town Kansas. Also I'm from Texas and piss like a racehorse was fairly common.
Southern US, heard police horse but racehorse is more common. But my family's was always "gotta piss like a pregnant woman" and "gotta piss so bad my back teeth are floating"
I once heard a coworker say: "if brains were gunpowder, they couldn't blow their nose".
A friend will occasionally say "that'll make you take back shit you never stole", which apparently means the thing (whatever he was talking about) was good.