From The Atlantic:

I'm at the Salt Lake City airport, and it probably won't come as a surprise to you that at least one TSA agent here thinks that sarcasm is just part of the job. I opted out of the new scanner--having looked it up now, it appears to have been a millimeter wave model--and was escorted over to the side after two agents gathered up all of my stuff.

"Have you been through this procedure before?" the agent asked.
"Yes," I answered.
"Just have to keep coming back for more?" he asked, somewhat to my surprise.
"You don't give me a choice," I said.
"Sure we do. You have a choice," he replied. "Scanner...or pat down!"
"I would have preferred to just go through the metal detector," I said. He paused.
"That's not a choice."
"I went through the metal detector on my way to Salt Lake City," I said. No answer.

"So what about the scanner is it that you have a problem with?" he asked
"Ionizing radiation," I said.
"There is no ionizing radiation!" he said, referring to his particular scanner.
"That's not true," I replied, not knowing which kind it was, since it's not posted anywhere on the scanner (and even if it was, I'd still opt out of anything beyond a metal detector). Also, the TSA's official phrases "whole body imager" and "21st century technology" say nothing about the use of ionizing radiation, x-rays, or terahertz waves; see http://blog.tsa.gov/2008/04/safety-privacy-concerns-regarding.html.
"What would you call ultrasound?" he asked.
"I have no idea what model or type of scanner that is," I replied. He proceeded to lecture me in a mocking tone as though I were an idiot.
"There's only two types: two flat boxes, that's backscatter x-ray. Round, that's millimeter wave. Flat boxes, x-ray. Round, millimeter wave. I don't blame you for not wanting to go near the backscatter, but this one's fine."
"Well, I've had six CT scans, so I really don't need any more radiation of any kind." (I'm aware of course that many things including visible light are part of the EMR spectrum, but I wasn't about to get into a debate over physics with the agent.)
"CT scans...those are local."
"Not necessarily," I replied. "And I've had two head, two chest, and two abdominal."
"Well, you could just do it to spread it all out." he said. He then ran my chap-stick through the X-ray scanner, and finally walked away, leaving me to think...what the hell?

So, it's clearly not the worst TSA story ever, but I think it highlights three points (which are nothing new to you):

A) the totally arbitrary nature of the scanner selection process;

B) that passengers' decisions to opt out should never be questioned as it's none of the TSA's business why I have a problem with the scanner, even though in this case I had no problem sharing why; and

C) that passengers' decisions to opt out should absolutely never be ridiculed, or even remarked upon in a manner that could be interpreted as ridicule.

Another thought that came to mind is that had I refused to answer the agent's question, depending on how obnoxious he was feeling, he could have said that I was refusing to cooperate. So either you disclose personal medical information to the government, or you're not cooperating. What a deal.