Funny Things You Can Write on a Birthday Cake. If you're tired of the standard "Happy Birthday", then check out these sayings you can put on a birthday cake instead. In fact, you don't need to be celebrating a birthday to write a saying on a cake. Just do it for fun! Surprise the family. Use the sayings as is, or use them to inspire your own creative sayings. #birthdaycakes #birthdays #cakes