Law professor Laura E. Little studies comedy and the law. She says jokes in a will can be subtle, but they're still funny. Law is very literal so parody doesn't get treated as such by courts.
In 2016, a man named Anthony Novak created a parody Facebook page of his local police department. "I just thought, 'That would be funny.'" About a month later, he was arrested. Novak is now petitioning the Supreme Court, and The Onion submitted an amicus brief in support of his case. Their brief is written as a parody of an amicus brief.