Is there some other trait that affects the mechanic?
I've noticed the goofballs in my game have very different toilet pranking frequency.
Baako Jang has only pranked toilets twice in about 4 sim-weeks of played time for his household. He never pranks a toilet (that I've caught him at) when I'm playing another household and he's present on the lot as an unplayed sim.
Billie Jang has never pranked a toilet either as played or unplayed. (She's been a teen now for about a sim-week and a half, so any limits on children being unable to prank toilets wouldn't apply)
There was a neighbor Keiko Morita in 19 Culpepper who was a goofball. She came over as a visitor to the Rasoyas and the Bheedas all the time. She would prank a toilet on EVERY VISIT. I never played her, she was a random townie. It got to the point where as soon as my sims saw her at the door they would quick go lock all the bathrooms.
I'm curious what would account for the differences.