<< Just be polite, this is what they believe in so respect them for that. They aren't trying to disrespect your religion, they're just trying to obey what they believe in. >>
I respect all people's beliefs and ideas. However, I consider it highly disrespectful, regardless of what their religion states to just show up at someone's door and pound away until they get an answer and then continue to persist despite the fact that your "target" has already explicitly stated he is not interested in what you have to say.
It's rude enough just to show up someone's door announced. It's doubly disrespectful to say "Do you want to hear about my faith?" and then persist when I say "No, thank you." Evangelism is one thing. I evangelize when the opportunity presents. Pushy is different. I know pushy Christians, too. They're just as bad. If the topic comes up and someone says "I don't want to hear it" then don't try and make them hear it. Respect them and maybe they will respect you finally.