I stole some from the neighbors when I was 12 and then periodically from my little brother when he was a baby. The first time I bought some that fit me was a really awkward experience. My older brother was home from boot camp and went into his bank to deal with some issues and so I went next door to the supermarket and bought some store brand diapers. It was a horrible experience, they wouldn't ring up and then they wouldn't fit in my backpack.
I ended up telling my brother that I was buying them as a part of a lame 50th birthday gift for my dad. I hope he bought it, but then after the fact, I went in the back room and put one on. There's a good chance he thought something was up, but he's never said anything. Then, since this was the first time I had worn a diaper that fit me, I got super excited and decided to mess it. Big mistake. That sh!t stunk. So, I cleaned myself up which was a lot more work than I thought, and I decided to dispose of it by leaving it in the backyard. Unfortunately the dog played back there, and dogs love things that stink. So, I had to come up with some kind of means to dispose of it without anyone noticing or the dog eating it. I eventually took it into the woods behind the house and just buried it. That was a highly educational moment for me in maintaining my secrecy and exercising caution.