When people come to the door I look through the peephole. When it isn't the mailman or someone I know (and want to talk to) I won't answer. That's just how it is.
When the person at the door is carrying a clipboard and looks to be wearing a nametag, I sure as hell won't answer.
When that person rings the doorbell another 4 times and opens the screen door to bang on the door, I get freaked out and a little angry.

I just flung open the door and screamed "WHAT THE *FUCK* DO YOU WANT?!" at a kid selling magazines subscriptions for his school. And he STILL tried to cajole me into a subscription.
people always amaze me.