𝙳𝚊𝚒𝚕𝚢 𝙵𝚒𝚜𝚑𝚠𝚛𝚊𝚙You know the saying about ten gallon hats...
Edit: in case you don't, there's not a lot of examples of the insult. Two variations:
"Mister, that's a ten gallon hat on a two pint head"
Or, from a scene in the TV series Justified:
"Mister, that's a ten gallon hat on a 20 gallon head."
Plus the usuals... "All hat..."
Frank