Badmouth Your Clients
One Starbucks employee was fired when a (actually quite clever) YouTube video of him singing criticisms of customers reached Starbucks executives.
Call it hypersensitivity, but don't even badmouth your client’s hometown! The day before a meeting with FedEx, advertising executive James Andrews dissed the company's hometown, Memphis, via Twitter. He and his agency were forced to make a public apology.
A better career move: If you are steamed about your treatment by clients and something needs to change, take it up with your superior and brainstorm ways to improve the situation. But when you're in public, sometimes you just need to put on a smile and kvetch to your friends in private.