I read this AU where Levi and Petra are married and they have a newborn baby so they move into a new house. But the house next door is a college fraternity owned by Eren. Levi and Eren form a rivalry and pull pranks on each other. Then one day Petra goes over and apologizes on behalf of her husband and makes them cookies. But the cookies end up having laxatives in them and Levi just couldn't be more proud of his wife for making those college kids shit their pants.
I think it is a headcanon written by textsfromtitanfood but I don’t remember the part where Petra gives the cookies.