Simply outlaw Bitcoin and declare anyone who is still using it an enemy of the state and threaten them with a lifelong stay in a cozy prison cell? I think this will be quite the persuasive argument
![Grin](https://bitcointalk.org/Smileys/default/grin.gif)
People would stop running nodes, the exchanges will cease to exist, peer-to-peer sites would be either monitored or shut down as well etc.
The easiest way to kill anything is to kill the infrastructure and everyone will stop using it sooner or later when it's no longer convenient.