Oh, PTerry, you rapscallion!

In "Thud!" when Brick (a troll) is about to be questioned by the Watch. He says "I'm in deep copro, right?".

Now, I've heard of coprolite somewhere so I got that "copro" was a reference to that. So, I go and look up coprolite and what do I find?

Coprolite is fossilised feces.

Yeah, Brick is in deep shit.