I opted out last year, not because of radiation (couldn't care less about that), but just because its a nuisance to them.
They did ask me why I wanted to, so I said "I wasn in the mood to get a dose of radiation today." The TSA agent got on her walkie and said we have a male opt out. I've heard they'll scream this out to try to embarrass you, but unfortunately she just did it on her walkie. I waited about 1 minute, then some male TSA agent escorted me to the other side of the scanners and then asked if I wanted to step in this private pat down room they have, I said no just do it right here. He then began to pat me down. We had a short friendly conversation during the groping session, and then it was over.
I made an effort not to be rude or condescending, as j think that's what gets most people into some bad situations with the TSA. Theirs some bad eggs, but I would say just peacefully opting out will net you a positive groping session mos of the time. I don't like the people who do it looking for trouble, it gives us a bad name and we stoop down to their level.