Was he showing non-verbal signs of pain? (grimacing, flinching, etc) You could document that, or a lack of that. Did you do a pain assessment (PQRST)?
Did you speak with the Pt.'s RN or CNA? (to find out if this was a common pattern...ie did the PT have a routine in the morning that wasn't being followed, etc) Did the Pt just want to work with someone they knew? What was the patient's complaint? Did he say why he was refusing?
I've worked with developmentally delayed adults as a caregiver. Lots of times, my clients were just tired of being told what to do. I found if I chatted with them and figured out what THEY wanted, sometimes I could combine what I needed them to do and what they wanted to do.....then everyone's happy.