Are you curious for what your friend or neighbors doing privately?? Be a spy!! Spy on your victim through his webcam, record the scene, then show a compilation of his private doing's.
You can do this through remote-monitoring programs, such as WebCam Monitor on Windows; and even do it through an iPhone using Telekinesis, an iPhone app that allows you to take pictures on a Mac laptop using its built-in iSight camera.
Reminder: Im not responsible if you get caught on action.