Lose Your Marbles: Go crazy, lose your wits.
I believe that man has completely lost his marbles.
From Phrases.org.uk: It’s … likely that ‘marbles’ was coined as a slang term meaning ‘wits/common sense’, as a reference to the marbles that youngsters play with. The notion of ‘losing something that is important to you’ appears to have migrated from the image of a forlorn child having lost his prized playthings. An early citation of this figurative usage is found in an August 1886 copy of the St. Louis Globe-Democrat:
He has roamed the block all morning like a boy who had lost his marbles.