This is a joke. It is meant to be funny.

There's a nice boy named Sherman.

There's a not nice girl named Penny.

Penny gets her way by calling Sherman a dog. That's not very nice.

Penny is going to be in a painful wedding.

Sherman wants to save Penny because he is a nice boy, not because he has a crush on her.

Sherman is not in love with Penny.

Sherman rather would spend time with someone who is nice and not mean.

Sherman is a very nice boy and is only friends with Penny.

He holds no romantic feelings toward Penny.

Joke/crack. Don't take this seriously when it was intended to be funny.