Here is my model in normal state. No deformations.
The second I rotate at this point we get this deformation. No other part of my mesh has this problem.
Here is the same mesh but backwards.
Here is the weight paint. It's mirrored on the other side.
And the geometry if it will help.
It looks as if something is stuck there and is causing this problem. looked around the problem area and I can't find any out of place geometry. Any ideas?
Link to the .blend file. http://pasteall.org/blend/32923