I wear an insulin pump and I never use the term opt out. I always tell them I can't because of the insulin pump. That's a medical reason, but I always get the patdown. More airports seem to just let me get my grope, swab my pump, and let me be on my way.
Every so often, I get the lecture about how safe the scanners are, less radiation than 2 minutes of flight, less radiation than a cell phone, etc. Those drive me crazy. I've even been told to tell my doctor that he wrong and that I should go through the scanner. It's the manufacturer who says not to go through the scanners. There was a teenager last year at SLC that had her pump damaged by the scanner, so I'm not taking chances.