WTF did I do to my AR?!

Looking down the barrel towards the butt stock left (counter-clockwise) would be loosening, however that barrel nut has not loosened.

 

Why not contact your friend and the shop? If I'm not mistaken don't some of the older MI rails have a habit of twisting? My friend mentioned that when he was installing his, I think they updated the design to fix the issue.

 

This is a common installation problem. I've done this myself. The bolts were over torqued. You need to use a torque wrench to apply the proper amount of force. On the plus side it's mostly cosmetic as those tabs are for alignment purposes only, however it looks like complete and utter garbage. I recommend any rail system that does not use this system AND using a torque wrench.

 

Make him fix it if he values his reputation. That is one good thing about gun shops they get a bad rep they are finished.

Lot of you tube gunsmiths that have no clue what they are doing.

Let me guess shop that is located before the strip? I know your AO well.

 

This times two. He'll have to back the barrel nut off just a little to get everything lined back up but the tabs on the forearm are toast. It'll probably function fine but for what you paid, they shouldn't be broken.
I'd ask him to replace it.