Originally from: Chocolate beans, an item that spoofs jokes.

It's a joke on you, implying that you are a pig.

Another similar one is: It's your birthday, pig, happy birthday to you (happy birthday to you).

I have also invented a similar spoof oh, published here, haha, you can use it to fight back:

There is a smart child, there will inevitably be a stupid child, the smart child is me, the stupid child is who? The answer is you, because there is a thing called: I stupid egg (quail eggs)