That's a good one!
I though you were heading for an ending that happened to me about two years back on one of the heavily overhung freestone creeks up here in the Poconos. Here it is.
Like you, I was with a fishing buddy and also like you, I was having a pretty good day and he wasn't hooking up at all; although he was casting to the right spots and he'd been fishing that same water for many years. Since he wasn't catching and I was, he was positioned upstream of me as we continued to move in that direction, was getting a little down due to no fish, and he also hooked a pine or rhody on one of his backcasts. He'd been fishing, exclusively, his "swear-by " fly, a small Henryville Special, which is an over-dressed, but very popular fly up here on any water that's on or close to Broadhead Creek. I'd suggested changing flies earlier in the day; several times in fact, but each time I mentioned it, I got a progressively stronger hand pushed my way, a head shake and a quick cast to a new spot with his tied and true HS.
He was not really interested in walking even a few steps downstream to try to free the fly and was just standing there, body turned downstream, yanking on the line; sooner or later, he was just going to snap the tippet; we were fishing light gear; 3 wts. with 5X.
So, I put down my rod and walked upstream motioning to him that I'd free his fly; he didn't seem to object to that (at least he was going to get some free service to help compensate him for his lack of fish). When I got there, I reached up (you've got an inch on me) pulled down the branch, snapped off his fly and quickly tied on a soft hackle that I'd been using with good success all morning (Stewart's Black Spider).
While I was tying on the new fly, I made it appear like I was pretty frustrated with the whole rescue of his fly, then I motioned to him that it was clear, shook my head and told him to cast out again.
He did - and he got a strike on the first cast!, and landed a pretty little rainbow that put up a reasonable fight for a small fish. When he landed the fish, netted it and went to remove the fly, he paused (realizing now what I'd done), demonstrated that his middle finger was still properly positioned on his hand and then put down his rod, smiled and gave me deep, comical bow!
I never got the fly back from him.