I don't worry. I wasn't asking about everyone else's habits. I go through metal detectors multiple times a month and have for decades. I have my experience and habits, too. The detector was ridiculously sensitive this time. In my original post I wondered if this is the new normal at DCA.
Judging by my overall experience and seeing that nearly every other guy besides me was setting off the alarm, I know it wasn't just me. As far as whether this is the new normal at DCA or not, I'll be going through that same line again in a couple weeks, and I'll get another data point. This hat will stay at home, though.
Sorry, my post was meant as subtle advice, not as a non-sequitur reminiscence.
The "new normal" for the last 17 years is that there is now no such thing as "normal". The screening experience changes minute-to-minute depending on the individual TSOs manning the c/p, as well as their local supervisory hierarchy (leads, TSMs, FSDs) and the current set of ever-changing policies issued by TSA HQ in DC.
The best way to ensure, or at least increase the likelihood of, a screening experience with no alarms or escalation, is to prepare for the worst-case scenario. Since most things in life fall somewhere between best-case and worst-case, being prepared for the worst-case means you'll never be under-prepared.
Hence, my observation that I always empty my pockets and doff my belt and outerwear no matter which screening methodology I might encounter at the c/p.