Green’s Dictionary of Slang

squirrel-shit adj.

also squirrel-shit nutty
[the idea being that a squirrel’s excrement is extremely nutty adj.2 (2)]

completely crazy, mad, eccentric.

[US]J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) I’m a skin man! I go squirrel shit if I don’t get no skin!
S. Nicholson Farm 372: ‘Gordon’s gone squirrel-shit nutty,’ Jett whispered to Katy. ‘I think we all have,’ Katy whispered.