I look to see who it is and I keep playing my Xbox360, computer, and watching TV even though they have saw me. I let my dogs bark at them until they leave.
First thing to do is look at how they got there (their car) hopefully to see if they delivered something. Then look at the person through the peep hole in the door. If you're not alone, you could probably open it (or get someone else to open it).
I'd open it.... What if they needed something? I'd invite them in and have tea with them. If they didn't like tea, then they're going to have to deal with the baseball bat >
As you open the door shout "FOR THE LAST TIME,I ALREADY PAID MY TAXES!" or "I DIDN'T STEAL THAT CAR!" or "THIS IS SPARTA!!!" and kick them down the steps!
or, if you are worried they might hurt you, before you open the door shout "I LOVE THE SECOND AMENDMENT!" and have one hand behind your back as you open the door.
I would drop to the floor like and creep the window like a ninja. Then I would see who it is. If it was someone I didn't know, I would get back up and take a nap on the couch.
Personally, I don't answer it. I don't know them, so why would I want to let them in my house? Though that knocking back idea is pretty good; I'll try that next time.
I would open the door and just stare at them for like 30 seconds and then just go back inside. Lol it's just funny imagining all these thing actually happening haha!
I live in an apartment so if people knock on the door it's usually my parents, my grandma or our neighbors, but I get suspicious so I usually don't answer. My parents and my grandma have the key so I don't need to open the door and our neighbors rarely come visit. So I just ignore them and hope they go away.