Disconnect external monitor without unplugging Mini DisplayPort Adapter Would like to disconnect my external monitor without unplugging the Mini DisplayPort Adapter. Any ideas? Running Mountain Lion, mid 2012 MacBook Pro.

The scenario: 

I have another Windows machine connected to this external display via VGA. So when I switch to my Windows machine, I would like to use the MacBook Pro without extending to the external monitor. It's too much an hassle to keep plugging out the Mini DisplayPort Adapter every time I switch. 

The Windows machine has VGA connected all the time, but it has an option to select a laptop display only mode without extending to the external monitor. 

Thanks.
Do you mean you want to leave the secondary monitor plugged into the computer, but not use it?

You can go to System Preferences > Displays > Arrangement and check the Mirror Displays checkbox. Make sure your primary display is set to the laptop's built-in display. Then just shut the secondary monitor off (so you don't see the mirrored display).

Now all your windows will be on the primary monitor and you won't be able to drag any to (or open any on) the secondary monitor, but it will still be plugged into the computer.