My cousin, the author Rachel Vail, has a family rule called "plums are not a one-bite food." At the home of another friend, there's a rule called "nothing, and no one, rides the cat." Chez moi, we have "yogurt is not a finger food." You can imagine the events that led to developing these rules.
Basically, the moment your baby can sit up, you find yourself saying the darndest things. Sometimes with a straight face.
If you like this stuff, let me also recommend the short video series, "Conversations with my two year old" where a real dad and another grown man act out actual conversations between a parent and toddler. (the little pink barrette makes the whole thing).