A friend of mine rented the upstairs of a house. Because of the conversion, the bathroom was in the hall outside their front door.
Larry was using the bathroom when he heard someone knock at the front door. His wife answered the door, and was talking to Jehovah’s witnesses. Larry stripped, and walked into the hall naked, then squeezed passed the people at the door. His wife told me their expressions were priceless.

I hid behind the arm of the sofa when a salesman was knocking at the door because I was naked.
I have hidden behind the door to surprise my husband. I was wearing a couch as I wanted to seduce him.

Pressing my ear against the door, to listen what is going on.
Clandestinely looking who is outside.
Waiting for a second knock/ring.

That is my usual modus operandi.

I have a nest cam with a speaker. I can tell the Kirby sales people to go away without opening the door. I did it from work a year or so ago. Dude started pitching over the camera which I just stopped monitoring.

The living room bay windows look down on the sidewalk as well as the front door. It’s a simple matter of opening the blinds. When the bell rings, it’s a peek through the window and then throw open the window. Depending on the view it’s “I’ll buzz you in”, “what do you want?” or “I have both a gun AND a mean dog.”

My next door neighbor’s teenage daughter knocked on my door while in her underwear and she was hysterical, asking for help because she thought she was in danger from her parents who were on drugs. I called 9/11. Well it turned out that her mom was a drug dealer and was under house arrest and she had violated house arrest twice. I didn’t even get the full story afterwards and to this day I don’t know wether the girl was being genuine or acting

One time when we were kids, there’s me, my younger & elder brother together with my mum watching telly of an evening.
A knock at the front door is immediately followed by it opening & an old drunk bloke stumbles into the living room.

He quickly apologises, realises he came to the wrong house & leaves just as swiftly as he came.
We all looked at each other, shrugged our shoulders & carried on watching whatever crap was on.
I laugh long & hard thinking about our nonchalant reaction!

I have jumped a bit because it’s unexpected, but I always answer it.

I could talk to the person through the security camera, but I think that’s kind of creepy and rude, so I answer the door.

One Halloween, I was at a friend’s house. A couple Trick-or-Treaters knocked at the door when I was standing next to it. I opened it and, before they had a chance to say anything, in a gruff voice asked “What do you want?”. The baffled/nervous looks were priceless.