As well as the breakfast hockey pucks which Lady's Human mentioned, there's the gingerbread story.

When we were kids, my beloved Grandma lived with us for a while after Grandpa died. Well, you know the "too many cooks" thing? Grandma and I liked to cook together, and made gingerbread many times. Then came *that* time. We were out of brown sugar, so made some with molasses and white sugar - not completely successfully, but that wasn't the big problem. We were both doing things too quickly, and as we poured the batter in the pan, I looked at Grandma and said "Did you put the baking powder in?"
"No, she said, "I thought you did!"
"Oh, I said, "I thought YOU did!"
So we measured the baking powder and tried to stir it into the batter already in the pan. Do NOT try this at home, boys and girls! It was awful. It looked like an amateur diorama of some ancient landscape, high in some places, low and gummy in others. We literally didn't gingerbread again for years!