Macbook Air 2013 rotate screen?
You can rotate your MacBook Air screen using the OS X system preferences. What you need to do is:


Launch System Preferences (first quit it if it’s already open)
Hold down Command Option and click on "Display"
Look for 'Rotation' on the right side of the Display window and take your pick


If System Preferences is already open then holding down Command+Option doesn’t seem to make the Rotatation menu appear. If you run into that, just quit out of System Prefs and relaunch it.

(found on OS X Daily and found here on AskDifferent)



EDIT:

Cave! I had serous troubles on my MacBook Pro retina. Do NOT try this method described above in Yosemite (and properbly newer systems as well)

Read this:
I recently tried this trick again to rotate my screen and got stuck in a nasty situation. My screen is inverted and my 'Display' menu in System Preferences will not open, when trying to open the 'Display' preference pane it gives me the following error:

"Preferences Error Could not load Displays preference pane."

I have tried the following things to fix it, non of these work:


Removed ~/Library/Preferences/com.apple.systempreferences.plist and ~/LibraryApplication Support/Dock/desktoppicture.db, and rebooted.
Logged in as another user or as guest user.
repair permissions, gives the following warning:


User differs on on "private/var/db/displaypolicyd"; should be 0;user is 244
Group differs on on "private/var/db/displaypolicyd"; should be 0;user is 244

Installed the 'OSXUpdCombo10.10.3.pkg'
Re-installed 'OS X - Mavericks over my current system'
Manually removed the Display preference pane from /System/Library/PreferencePanes and installed the 'OSXUpdCombo10.10.3.pkg' after that.


Luckely I have an external display that does not go 'Australian' on me, but this is quite nasty. I am now preparing for a clean install of my system as I am out of further ideas.

EDIT 2: - Temp fix/hack.
This will not fix the broken 'Displays' preference pane, but it will help you to leave 'Down Under' and zero out gravity.
Rotate your screen using a third party app:

'Display Rotation Menu 1.2'


EDIT 3:
Complete clean reinstall of the system 'fixed' the issue. I have only restored the non-admin users via TimeMachine. 

Error message: