Temmie Tummy Ache

Okay, you little genius, let me break it down for you. You posted something on the internet, congratulations. The joke plays on the words "tummy ache" and "temmie ache", because the character is a Temmie and ate too many Temmie Flakes. Get it? It's a play on words, and it is meant to be funny, but you probably don't get it. Simpleton.