Doorbell rang. Saw through the peephole that it was JWs. Opened the door and said "Hi" in a friendly manner. The guy doing the talking was clearly surprised by that. He said he was looking for Spanish speaking families, and looked a bit confused. I said "We don't speak Spanish, sorry."
Regrouping, he then went into his presentation about why they were calling (encouraging people to read the Bible). I asked what group they represented (knowing full well), and when he said JWs, I said in a warm and friendly manner: "Oh! Well, thank you for coming by but your group has a 100% failure rate in all of its prophecies. You are in an apocalyptic doomsday cult. And, you've got to get out of it." He thanked me and they went on their way.
I will not pretend I am not home. I will not get into a full conversation. A short and sweet no thank you with just enough information to say "hey, we know what you are about, and it's a bunch of BS." I don't mind spending five seconds calling them out. I know I won't get to them. I know I won't change their minds. I don't care. I want them to know that people are onto them and we know they do NOT have the truth.
Sorry, but you can't go to people's doors talking crap and not expect to be told the real truth about "The Truth" (tm). Politeness and manners are important nontheless.