[WIladyconservative]

he could simply have been mad as a hatter, 'round the bend and bonkers.

You forgot that he went beyond the black stump! (common Aussie phrase for all yours above)

[Oztrich Boy]

You forgot that he went beyond the black stump! (common Aussie phrase for all yours above)

Actually incorrect: "beyond the black stump" is simply idiom for a place far from the big smoke (aka the city).

The phrases you are looking for are "mad as a gum-tree full of galahs",

"silly as a two-bob watch", "Kangaroos loose in the top paddock ", "a couple of snags short of a barbie", and the everuseful "dill".