I have had the same arguments with my SIL and her husband, and they cycle too! Bicycling Magazine's book, 1000 All-Time Best Tips states, "For right turns, hold out your right arm with finger pointed. Forget that business about signaling right turns with the left arm held up. It originated because motorists couldn't reach across to point out the right window." It just makes more sense to me, too. Sorry you had two frustating incidents this week!