What will happen if you file taxes as married if you are single?

Called tax fraud. And of course the return is signed and sworn to as true. Bad things happen when you break the law. Doing so where your directly offending the Govt would seem particularly foolish, as they clarly have the ability to respond in force. Clearly, the Govt, IRS, etc systems are well developed to discover such acts, especially any as basic as this, many, many ways.