you need:
yes, these hotkey shortcuts flip/rotate the screen.
Crap, now how do I undo it? 
*On edit: *Duh, figured it out (up arrow).
Idle Hands are the playground of the devil, what are Idle Thoughts the playground for?
Pranks! 
If you unlock the taskbar and drag it to the top of the screen before inverting the display, everything gets even more confusing.
That is deliciously evil.
I pushed “Tab” three times before inverting the screen and my kids disappeared. Don’t tell me how to undo it for a few days, I’m enjoying the peace and quiet.
The feature has been part of a lot of graphics cards for quite a while, though not necessarily part of the Intel chipset/motherboards/gpus and Microsoft notes they stopped including it in the OS after XP because the graphics card people were already including it in their features.
We don’t include graphics cards on the desktop units, but our field users have such cards on their laptops and occasionally put in helpdesk tickets because they accidentally flipped their screen and can’t make it work right.
We tell them it’s a laptop feature for sharing a screen with the client on the opposite side of the restaurant table (flip the screen, then lay the laptop open flat), then we tell them how to flip the screen back again.
–G!
That’s not a bug; it’s an undocumented feature!
I accidentally learned this feature when cat jumped on my keyboard. Found it practical when reading e-books (my monitor can rotate 90°).
You just named the reason I always shut it off–albeit we now have lap dogs.
You think that’s evil? I was going to recommend taking a screenshot of their desktop, and then flip it in a graphic program and set it as the new wallpaper. Hide the icons and autohide the task bar. Open up the mouse properties and get to the orientation options, and move the mouse the opposite direction of the way it tells you. Then flip it.
The screen will be upside down, but the mouse will move normally. However, you won’t be able to click on anything.
This is one of those tricks where everyone tries to one-up the previous guy.
My cat does this to me all the time by running across the keyboard. The first time, I googled (on my kindle, as using the screen when it was sideways was crazy-making), and apparently LOTS of people’s cats do this.
I used to get on people’s computers and enable the “Marquee” screen saver. I’d put on a harmless message such as “Hey! Who messed up my computer?”
Ah, good times.
Cute. I did this with the right arrow and then restored it, and all my maximized windows were on my second monitor (which is to the right) instead of the original.