Sean Penn is someone whose ability as an actor is matched only by his tendency to raise hell. He famously attacked Madonna with a baseball bat during their four-year marriage (Happy Valentine's Day, everyone!), but today's Letter of Note concerns a very different kind of violent outburst.
The full text of Penn's letter can be read here. The fact that he included 'God Almighty' in the list of names to be copied in should give you a fair idea of his mindset.