On keyboards that have the little 'Windows' key (let's call it WK here) down near the space bar, you probably know that you can press that key to open the Start menu. For example, Ctrl+Esc will pop up the Start menu, Alt+Esc will bring the next window to the foreground (4), and Alt+Tab or Alt+Shift+Tab will let you cycle through all available windows and jump to the one you select. It turns out there are several other handy (3) keystrokes like that built into Windows.
So if you had pressed Alt+F4 while playing a game, the game window would have closed. Just about everyone knows that Alt+Ctrl+ Del interrupts the operating system, but most people don't know that Alt+F4 closes the current window. This joke works on machines running the Windows operating system because Windows happens to define certain keystrokes (2) that work the same way in all applications. This is one of those jokes people play on each other - it's in the same category with squirting (1) flowers and exploding cigars. Keystrokes in Windows: Does Alt + F4 close an office's application and other ones in the same way?
