I can see where, if you're 24/7, after a while you may get so used to wearing your diapers that you might open the door without thinking about what you're doing.
But for those of us who do this for fun, of course we do it on purpose! Now, being completely honest, I've never done this at home. As mentioned below, I don't want some door-to-door salesman telling my neighbors about "the diapered guy down the street". Well, honestly, at this point in life, I don't even think I'd care what they all think but it would embarrass my wife to death so, that's not an option. And, same thing with regards to somebody delivering a pizza (or whatever). I have kids that are the same age as most delivery people, and if I started opening the door diapered it would probably get back to my kids.
Now, all of that being said, here's something that I have done that gives the same thrill that's harmless. When I'm out of town staying in a hotel / motel, I'll often keep my diapers and plastic pants on top of the dresser and my diaper pail in plain view in the room or the bathroom and be sitting there in a t-shirt and diapers when the maid comes to clean the room. I'll usually open the door part of the way and tell them "I'm not completely dressed, but you can still come in, it's OK" and be sitting there at the table working on the laptop, or sitting on the bed watching TV--not flaunting my diapers, but, not really hiding them either. And if there's any doubt that I'm diapered, seeing the diapers / plastic pants / diaper pail are a dead giveaway.
I've never had any bad experiences doing this, but have gotten a couple of grins.
Most of them have seen things far more weird / disgusting than me in my diapers. And that's another fun thing that I often do. I'll start talking with them and ask them "What's the weirdest thing that you've ever seen when cleaning a room?" I've gotten some pretty interesting answers!
When my stay is over, I always leave them a nice tip!