You cannot just skip the .NET Framework on the target machine - it is needed to run your program. The exe file, produced by the C# compiler contains MSIL, which is understood by .NET Framework, as opposed by the destination OS - be it Windows or any other.
Having that said, your best bet is to write an installer for your app and
distribute the .NET Framework distribute the .NET Framework along with it. When launched, the installer might check what is the installed version of the .NET framework on the target machine (if any) and respond appropriately by installing whatever it is needed for your application.
You can use WiX to author an installers.