I opt out every time that I fly, and I always request a public screening, because I want people to see me being patted down. It's amazing how many people still aren't aware that they have the option. I've talked to a few folks in line about it, and even convinced one guy to opt out after me. Set an example and be obvious about it.

Funny story - on my last flight, the patdown resulted in an alert for some banned residue on my clothing, so the TSA took me aside to a private cubicle, re-ran the patdown, came up clean, and then left me to pack my stuff up and go on my way. In this cubicle with me were two 5-gallon buckets filled with confiscated lighters and pocket knives. Someone thought it was a good idea to leave me to re-pack my luggage unsupervised in a room full of contraband with no additional security checks. I didn't take anything or do anything untoward, and I wanted to point it out to the agent who'd patted me down, but I'm sure that would have just flagged me as suspicious and I would get to expend extra time being thoroughly searched. If that doesn't tell you how hilariously bad security is, I'm not sure what will.