Green’s Dictionary of Slang

tonto adj.

crazy.

1999		Indep. on Sun. 27 June 9: Has the thought that she might go tonto [...] crossed your mind?
2002		Guardian G2 29 Mar. 2: This oddly elegant, utterly compelling, but frankly tonto ceremony traditionally takes place at a charity event.
2021		A. Parks April Dead 34: ‘[H]e didn’t deserve you going Tonto on the bugger. You punched his face so hard [...] he lost the sight in one eye’.
2023		A. Rawnsley in Observer 19 Nov. 🌐 What to do about this humiliating reversal – chuck in the towel, double down or go totally tonto – has triggered a Tory convulsion.