Yes, I've worn diapers at the airport/on the plane. An odd experience, to say the least.
I was wearing cotton sweats over my plastic disposables when I set off the metal detector. Twice. Then they wanded me, which I set off in two locations--my chest and waist. So after setting off the wand at the chest, they asked me what was going on--"Nipple ring" so they guy patted my chest until he found the ring and said "OK. And the waist?" I told him "Belly ring"--and this is where it got interesting. So he started patting my stomach looking for the ring (which he found) but also started patting over the plastic waistband of my diaper, and then gave me a suspicious look. He asked if I had any plastic baggies taped to my stomach--I told him no, and then whispered "I'm wearing a diaper. I'm wearing a plastic diaper." At that point he told me to step behind the curtain and take off my shirt and drop my pants. So I took off my shirt--nipple ring and belly ring present, and NO plastic baggies taped to my person. Then I slid down the pants exposing my diaper (wet, by the way)--he 360'd me, patted the diaper, said OK, and then let me through.
Of course, they also found my diapers in my carry-on.
Interesting experience. It was not too long after the TSA was formalized and airport security checks were heightened. I can't fault them--a pierced, tattooed guy with possible "plastic baggies" taped to his abdomen.
Finding my seat on the plane was also interesting. I originally had a window seat and the aisle passenger (and some other random woman)was already seated. Obviously I had to pass by them to get seated--I guess as I was stepping over the seated aisle woman she heard my diapers (and probably smelled the baby powder--I changed after the security check) and the gave me this sympathetic look--"Oh, sweetie...um, if you want to switch me for the aisle seat that would be fine...it'll be easier if you want to walk around or need the restroom." I took her up on the offer, and after about 3 hours on the plane, thanked her again after I had to change diapers.