I had a good friend (and even better customer) I used to play with and he had a bad habit of forgetting strokes. I am not sure if it was intentional or not, but I started doing what Sole Wolf suggests, calling him on it. He looked accusingly at me and said, "Are you counting my strokes?" While smiling, I replied, "Well, yes. You seem to be having trouble with it." We both laughed, but it ended the stroke shaving.