What does Alt+F4 do?

This is one of those jokes people play on each other -- it's in the same category with squirting flowers and exploding cigars. This joke works on machines running the Windows operating system because Windows happens to define certain keystrokes that work the same way in all applications. 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. So if you had pressed Alt+F4 while playing a game, the game window would have closed.

For more information visit http://en.wikipedia.org/wiki/Table_of_keyboard_shortcuts