What you said very likely went right over his indoctrinated mind.

You're much kinder than I am.

I had some Mormons and Jehovah Witnesses come to my door. I'm usually wearing my Foxhole Atheist sweatshirt (my comfy house shirt), and tell them, "no thank you" with a big grin. One time I was outside watering my plants when a couple of Mormons walked up. As they laid into their spiel, I told them what I was and I wasn't interested. I think they got the message; nice thing though one of them actually complemented me on my front yard! I took great pains to keep it looking nice, so I thanked him.

You told him correctly. in my area there are seldom any approaching you as you get out of a car but I get a lot of bell ringers from JW's and Baptists. The Baptists always want to tell me to "look at the trees" as their proof and I'm starting to ask them why they believe ancient sheep and goat herders knew of a creator god and yet did not know where the sun went at night. Visits become very brief.

I have come upon a few mormons teenagers here in Australia from the US who are over here to try to convert people. I have always found them very nice, ever so polite and happy to listen to everything I have to say. Not once were they annoying or rude. I kind of feel sorry for them.

Anne you posted this 4x. Delete the other 3 lol.

I had two Mormon kids knock on my door a few weeks ago. They used to come by all the time. It was 100° outside and they were standing there in their white shirts and skinny neckties. I went in the fridge and grabbed them 2 bottles of water. I told them I don't like to be proselytized to and told them to have a nice day. I wasn't gonna be mean to them. When it's that hot in Philly, it's also humid.

Good on you you have my adoration.
Unfortunately I don't think your message will make a positive difference to the lad. Most likely he will go back to his bullshit palace to learn a comeback and a turnaround.
I was bothered by the Jo Witless, they pestered me for over a year.
I found a skeletal goats head, mounted it on a board with an inverse pentagram painted in the background and sporting the caption, :" Come unto me ye children of Yod He Ho Ve for I am your father and master."
Funny thing, they never returned!