A possible summary is:
Marvin forgets his anniversary with Rosalina and gives her a wild rabbit as a gift. Jeffy gets jealous of the rabbit and bakes it into a cake. Marvin calls the cops to send Jeffy to his grandparents' house, where they have a room full of chihuahuas. Marvin gets another rabbit for Rosalina and pretends it's the same one. Jeffy tries to make another cake but Marvin stops him. Marvin gets sick and breaks the fourth wall.
Here are some key facts extracted from the text:
1. Marvin forgot his anniversary with Rosalina and gave her a bunny rabbit as a gift.
2. Jeffy was jealous of the bunny rabbit and baked it into a cake for his parents.
3. Marvin called the cops to kick Jeffy out of his house and send him to his grandparents.
4. Jeffy's grandparents have a room full of chihuahuas that they call kikis and they watch them like a TV show.
5. Jeffy's grandparents tried to feed him to the kikis but he escaped and ran back to his parents.
6. Marvin lied to Rosalina that he got another bunny rabbit and pretended the one in the cake was alive.