When I was much younger, about twelve or thirteen, I was visited by Jehovah's Witnesses. I had never experienced the Witnesses before and was quite unprepared. My mother had raised me to be polite to strangers though, and I was pleasant with them. My mother was also very religious and had raised me accordingly. My knowledge of the bible was more than adequate to duel theology with these missionaries.
I then spent many minutes quietly debating with them on my front porch. I was polite enough to not call them names, and they were resolved enough that they did not want to be outwitted by a pup. After they left, my mother came up from the basement and asked me whom I had been talking to.
I told her the story and added that they seemed a little confused, and a little pushy.
My mother replied, "Pay them no mind, they are confused. It doesn't hurt to talk with them; it may even do some good. But if you don't want to talk with them, just tell them you're Lutheran and they'll leave you be."
Strangely enough that works. I used to go on about how I was a Lutheran and how I would be more than happy to talk with them, but they always replied negatively and left quietly. As I got older and lazier I realized that a simple, "I'm Lutheran" works just as well.
I have no idea what their aversion to Lutherans is.