I didn't even know that a 7 month old could tell a joke, but here it is.
I was washing dishes and cooking breakfast for Bob while the boys were eating their oatmeal, and he was feeding Rosemarie baby cereal. She wasn't acting very hungry, and whenever he'd try to give her a bite she'd just say, "Mama. Mama." So he gave up on feeding her, and just left her in her highchair while he did his puzzle. After a minute or two, she said, "Dada!" So he turned back to her to give her another bite of cereal. Instead of eating it, she said, "Mama!" Then she looked at me and started laughing.