@MoonlightGraham
erratic sims don't prank toilets like goofball do. I'm not sure if the prompt to do so is in the mischief wheel for all sims but they won't do it autonomously like goofballs do.
Erratic sims will mostly
Talk to their invisible friends. Shower in the rain. They might randomly insult or yell at another sim. I have one erratic sim who never yells or insults while all others do. The mood swings are angry (flarn) sad (shmoo) flirty (elicanto whirl) and playful (oh be gah) moodlets.
Most of the time they talk to themselves or their invisible friends. That's the most used autonomously used action probably followed by showering in the rain especially in a rainy world.
Erratic sims, for me, are a lot less annoying than goofball. Way less.