Scary title, but not what you think. I see a lot of the guys at my gym (conventional big box gym, so very tight shoulders) doing Dislocates. Always with a weightless bar, usually with arching, and usually externally rotating the arms so they get stuck on the back. I help when I can.
The question: besides the fact they won't make progress this way, what other problems could arise from this form? Impingement was my first thought, hence the title.