It all depends on who's at the door and how they react. It could be easy as a smile and a nod or a complaint to the police, getting arrested and charged as a sex offender. One way to avoid that is to just throw on a pair of shorts and not worry about it. I have a pair of Uzi's hanging by the door for that reason (they don't cover much, but enough not to get arrested.) I actually have a sign that I can hang on the door that warns people I'm a nudist and anywhere beyond this sign you will encounter nudity. I haven't used it yet, mainly because I'm not sure I want to draw attention to myself and risk people intentionally looking into my house or yard so they can complain about seeing naked people.
Simply tell the person through the door that you are nude and ask if t's ok to open the door. Once they give consent you are safe. If not ask them to wait until you put something on. Once I ran out to meet the postage lady with some mail that need to go out that day and my towel fell off! In the middle of my front yard! Sometimes accidents do happen!
I live on a country road, so no direct neighbours and not much passing by cars.
I have anwerd the door naked when I know who it's gone be.
Last week a friend and his wife where come for a visit. They know I'm naked all the time and I can stay naked when they are at my place so I opend the door naked.
I haven't done it for unknown visitors.
Well I was obviously embarrassed. I bent over and grabbed my towel to put it back on and she watched the whole time with a big smile! I apologized and she said no problem and that it made her day. All her years on the job and had never had that happen before. From then on whenever I saw her she waved and winked, smiling of course!
I wish we lived in a world where this wasn't a big deal. If I know the person and they're cool with it, it's cool. Personally I don't want to put a person in an awkward position with my nudity; it can be counter productive to spreading the good word. Also, I work from home, and clients would not be okay with it.
With that said, if you make a reasonable effort to not impose upon people and someone sees you accidentally (either on your part or theirs), they would have to be a real douche to make a case out of it. In the city here I'm pretty sure everyone has seen everything (anatomy, body function/fluid) at some point, in public or incidentally, delivery person or not; everyone laughs it off. I bet most delivery people understand that they're entering people's private living space.
If I lived in the country maybe I would feel different about it. I think in the city you really need mutual respect with your neighbors to make sure everyone is comfortable (there are probably 12-30 people living within 100 ft of my apt (depending on how you count, which is common here.).
I have answered the door nude when a friend who has seen me in that stare before called. The back door if most often unlocked for family and friends to just come in and they have while I was not dressed, and our letter carrier saw me in the kitchen once when she dropped a package inside the back door. At other times I have wrapped in the blanket that I keep on the sofa, but it is also rare that anyone comes to the door.
One day, I went to the door to see iff the mail had come. I opened the door and there was our female letter carrier. I said I was just checking to see if you had arrived. She said she didn't know I was there. A giggle and she left.