I think what offends most people about JW or COLDS(Church of the Latter Day Saints) is the fact they are not knocking on your door and simply giving you a message...they are knocking on your door time and again and being annoyingly persistent in their messaging. One cannot beat someone over the head with a Bible and convince them to accept Christ. I've had area churches that knock on the door and politely invite you to their church and give you a paper with the times of their services and their mission statement but they do not try to convince you to follow their doctrine on your front porch. This bothers me not the slightest. For that matter, JWs do not annoy me either but I know they annoy the heck out of most folks.
It would be much the same level of annoyance with any religion that repeatedly assaulted your privacy and insisted you listen to their ideas about faith....imagine a Muslim or Atheist or Messianic Jew showing up on your doorstep each week trying to get you to listen time and again. It is not the message they deliver that annoys people, it is the method which they use that does this. One cannot force someone to convert to Christ. Even Christ did not go door to door, he went town to town in open arena or in the synagogue or temple.