Usually I scan driver’s seat or the rear driver side seat to check for doors that might opening ahead of me. In this instance, a passenger in the rear reached over the seats to open the rear, driver-side door. I didn’t anticipate it at all. Had he swung the door all the way open (or had I been a less experienced cyclist and got spooked), there would’ve been an accident. Silver lining: He apologized! Unlike this guy. So, that was nice of him.