RORY: Where should the poached eggs go?
LUKE: Crank in the hat.
Crank is a term to refer to someone with an unshakeable belief in something that most of their contemporaries believe to be false. The term was popularised in 1872, being applied to Horace Greeley in his campaign for the US presidency. He believed in the settlement of the Old West and a magnanimous Reconstruction of the American South, and was a proponent of socialism, vegetarianism, agrarianism, feminism, and temperance. Cranks today can take comfort in the fact that all Greeley’s cranky ideas were proven very sensible, and are mainstream today.
In North American, a crank can also be slang for a bad-tempered person. I’m not sure which one Luke was applying to Cy, the “crank in a hat”, but Cy seems to believe it’s the second one, because he makes a spirited defence by saying that Luke is the crank – he’s well known around town for being grumpy.