an expression to tell how
annoying somebody/something is, as much as something probably very messy.
The reference to a "thick piece of shit" and the fact it is no fitting for a "shallow bucket" probably comes from a real life experience most likely to have happened at the beginning of the 20th century and those before, when modern
time toilets were nowhere to be seen in farmhouses and camping grounds of
America.
Guy 1: I truly think you should not
play with matches that close to the gaz
tanks...
Guy2: shut up, you're as
annoying as a thick piece of shit in a shallow bucket!!!