The ScreenBouncer application is a part of the prank collection that will make your monitor bounce!
You cannot close ScreenToys in usual way, because these programs doesn't have a Close button. Alt+F4 is not affected with this program, even Task Manager cannot stop these programs because ScreenToys always run topmost from another windows.
To stop ScreenToys, move your mouse to top-left corner of the screen. A message will appears that tell your friend if it is only a prank. Click Close button and prank is ended.