After crafting a shit nugget, you cannot use the same toilet again right away. However, sometimes you want to prepare for the upcoming battles. So how long is the cooldown of the toilets in the game or what triggers it to reset?
All you should have to do to craft another nugget is leave the bathroom and then come back into it. If this is not working then just go bathroom hopping. You can even make a nugget in a urinal if your in the right bathroom ;)