Option #1: Press Command-Option-Esc keys to force quit full screen app

To open “Force Quit Applications” on a Mac OS X press Command-Option-Escape:

Select an app (say VLC) and press “Force Quit” button. You may be prompted as follows:

Option #2: If you cannot switch from the unresponsive app…

If you cannot switch from the unresponsive VLC app, press Command-Option-Shift-Esc for three seconds to force it to quit. This key combination tells OS X to force quit the frontmost app.

Option #3: Bash Terminal killall command option

Open the Terminal application and type the following killall command to kill the VLC app:

killall -9 {app-name}
killall -9 VLC

If you do not know the exact name of app, use ps command as follows:

ps aux 
ps aux | grep -i vlc
ps -xu username
ps -xu vivek | grep -i vlc

References

• OS X keyboard shortcuts