I look scary.
That's the only explanation I can think of, plus two friends have told me that they thought I was a mean sonuvabitch when they first saw me, before they got to know me.
Absolutely every time I have flown since they've started the extra security measures, domestic or international, I have been selected to have my carry-on luggage checked at airport security. I have been told that these checks are random, that they pick every tenth person. That's bullshit, and one of the security folks told me they just pick someone who looks like they'd like to blow up an airplane that day.
Apparently, that's me. I'm a 6'2", 250lb gent with a buzz haircut and a goatee. I usually have a tan because of my Italian heritage. I don't have the build, but I've been told I look like Stone Cold Steve Austin after he came home and found his grandmother was eaten by rodents. I usually wear Doc Martens with steel-tips (because they're comfortable and I wore steel-tipped boots for years while I was in the military). When I fly, the airlines usually screw something up, so I don't have my happy face on when going through airport security.
I have the routine down. The carry-on goes through the x-ray machine, and it's filled with electronic stuff. The security person (normally an African-American woman, I don't know why it works out that way) picks up my bag while I'm stuffing my watch, change and Harley-Davidson wallet-on-a-chain back into my pockets. "I would..." they'd start to say.
"You'd like to conduct a routine security procedure on my baggage, which involved rubbing a patch on the handle of my baggage and inserting it into that machine over there, which will scan the patch for traces of nitrates and gunpowder," I'd finish for them. "Be my guest."
I haven't had the balls to do it yet, but one of these days I'm going to go target shooting just before flying, and perhaps rub some gunpowder on the bag itself, just to watch the machine light up with alarms and to watch the security guard's reaction.