Every 5 year old will say this at one point, whether it's when they take a big shit and it smells, or they watch a movie with a million fart and poop jokes.
To leave a shit that is unexpectedly stinky and intentionally failing to flush the loo afterward; the unflushed poo really fucking reeks and makes the bathroom stink to high heaven.
Johnny retaliated for his mother asking him to clean his room by going into the bathroom to leave a stinky.