Green’s Dictionary of Slang

squirrel-shit n.

In phrases

nutty as/nuttier than squirrel shit [i.e. extremely nutty adj.² (2)]

(extremely) eccentric.

2000		Guardian 9 Sept. 3/1: An audience as nutty as squirrel shit.
2006		M. Harper Who Am I to Complain 22: His exploits were legendary mostly because he was ‘nuttier than squirrel shit’.
2008		F.J. Roberts Apocalypse in Mind 9: Yeah, he was nuttier than squirrel shit. No doubt about it.
2011		Vancouver Sun (BC) 27 May 38/1: Gregg Araki’s latest film, Kaboom, is [...] in one character’s words, ‘nuttier than squirrel shit’.