I brushed him on the back patio so the extra fur wouldn't be left in the house. After I put his collar back on him, he took off as fast as his little legs could carry him, straight toward the CLOSED sliding glass door (dunno why; we'd used the hall bathroom door to get there), and ran, nose-first, straight into it. I think he was more surprised than hurt, because he got right up and looked at the door like it had just materialized out of nowhere. And then looked around as if to say, "Nobody saw that, right?"
He doesn't seem any worse for the wear - he's not yelping or refusing to let me touch his nose, so I think he's ok.