David, look at the power she exerted over you. I think that while you think her celebrity evaporated in that moment, what really happened was that you inflated it and let your defiance of it cause you to do something that you now see as rude. At the price of a few seconds of turning her back, she has for years given you a single moment to fill hours and hours of navel gazing, which after all those years has become almost self-loathing.

After years and years of contemplating my own regrets, being not much younger than you, I agree with jp498. You really need to forgive yourself for this.