Naruto insists on paying Sasuke a rent. Every month without fail It appears in random places, piled on Sasuke's bedside table, sitting on the table with his morning coffee, rolled around his toothbrush, or even, on one memorable occasion, in his underwear.
Without fail, it is returned to its owner.
Being slapped in the face by a wad of bills loses its shock value after the third time.
So they fight, and Sakura sighs, and kicks them out of their house. It might have been Sasuke's house at first, but it's home now. Their home. Naruto doesn't understand that being paid for the right to keep on living with them makes Sasuke feel like Naruto is his tenant and not his teammate, his mate, his lover, that Sasuke didn't pay for this house and he doesn't like getting benefits out of it. Sasuke doesn't understand that Naruto doesn't understand how it works with family, that he needs to feel useful, that being taken in makes him feel like a housewife who can't even do the chores right and even less carry his child -- like he's a stray, only there by charity.
Naruto needs to repay Sasuke for taking him in and Sasuke can't stand getting money from family.
Sakura sighs, and takes the money for the groceries. Boys, she thinks, no practical sense, and pulls Naruto aside for advice on how to get around Sasuke's mule-headedness.
Somehow, Sasuke has a much harder time to refuse rent when it comes in the form of free coupons for one night of the sexual fantasy of his choice. A good thing Naruto doesn't see anything wrong with being a prostitute for his lover.
Sakura participates for free, and still feels like she got the better end of the bargain.