“As daft as a Coot”

I always thought that the common idiom was “As bald as a Coot”, so when my dad said “As daft as a Coot” I was surprised. Daft means silly in British English. What exactly is silly about Coot?

Nothing.

Now I find that Coot are subjected to all manner of other insults, including “Queer as a Coot”, “Dizzy as a Coot”, “Drunk as a Coot” and “Pissed as a Coot”, with ‘pissed’ meaning drunk in British English.

It remains unrecorded what Coot think of humans.