Green’s Dictionary of Slang

shit a brick v.

also shit a giraffe, shit bricks, shit nickels, shit peach pits, shit pickles, shit snowballs, sweat bricks
[shit v. (1a) + fig. use of SE brick/bricks]

1. [late 19C+] to defecate after a lengthy period of constipation.

2. [1930s+] to tremble with extreme fear.

3. [1960s] to be absolutely delighted.

4. [1960s+] to be furious.

5. to confess (through fear).