Arthur Ransome’s characters have some out of date but still appealing ways to describe their own, or others’, stupidity.  I had never heard ‘galoot’ before reading his children’s books, and quite like the combination with ‘mutton-headed’.

Use freely if you are looking for new ways to admit to stupidity, and here is a variant.

”We were a pair of mutton-headed galoots to go through the ice like that,’ said Nancy, hopping up and down.’

Source: Arthur Ransome, Winter Holiday (London: Vintage, 2012), p. 43