If you have been using the Mac for awhile, then you know at least one way to kill a misbehaving and/or unresponsive app. The method most folks know is ⌥ + ⌘ + Esc (Command + Option + Escape) and then (wait, wait for it) choose the unresponsive application (appears in red) in the Force Quit window, and click/tap Force Quit.

There is a one step version of this Force Quit method and all you have to do is add a key to the sequence: ⌥ + ⇧ + ⌘ + Esc (Option + Shift + Command + Escape), hold it for three seconds and the app should quit.

Alternately, you may be able to Option-right-click the application’s icon in the Dock and choose Force Quit from the contextual menu.

There is a fourth method that requires a few more steps. In the Utilities folder, open Activity Monitor, select the misbehaving app (appears in red) from the Activity Monitor window and click/tap Quit Process.

via Apple’s Mac OS X: How to quit an unresponsive application using Force Quit