In the 20s, the builders, when they were doing brick laying, they didn't have places to
poop so it became
popular to just poop in somebody else's
bricks because you wouldn't want to poop on your own bricks because you would have to put those bricks up.
It is used modernly as a term of warning.
Person A: I don't have anywhere else to
throw this trash so I'll just drop in on the
floor of your car.
Person B: Don't shit on my
bricks, mate. Shit on your own.