The End of Faith by Sam Harris is a great book and you are correct, it is a college level read. His challenge to you was just the sort of reaction you get from a conservatively religious person in public..pushing there chest out and acting like 5 year olds. Ugh. I feel for you man.

I would have told him, "I don't care if you think I'm open minded or not."

Your error was getting into an argument with him at all. how did you even get into a conversation where he brought it up? I would have been very firm and said “thanks, but I don't enjoy discussing religion and I sm not comfortable sharing my views about it with you.”

Challenging them back would look like that logical fallacy, what was it's name where you're not actually responding to the argument.
I can't even read all bullshit churned every day but they bring nothing new.

So my response is usually, sure I will but let me look at it's summary or review or notes. And then I delineate the propagandist logical fallacies used which are a common repetitive string or theme among any religious/zealot imaginative unreasonable ideology there is.

In this case, it is saying nonbelief is equal to different forms of belief. And that open mindedness to scientific observation testing and peer review doesn't mean to be open minded to believing shit at face value.
I'll tell them that as a conclusion he has the right just not to think about it and follow the parents and local church.. but if he does choose to critically appraise religion God and logic ,here are a few sources and here are the main arguments ,if he himself wants to be open minded too.

I think it's the "I thought you were open minded" argument that makes me angriest, especially because it tends to come from people who have never challenged their own internal biases and blind spots or examined evidence that challenges their existing worldviews in a critical manner. Specifically where faith is concerned, I had 12 years of religious education and more than a decade of my own spiritual exploration before reaching the conclusions I have; I can virtually guarantee there is nothing in a proselytizing book that is going to provide the evidence for God that I missed and draw me back in, and I am under no obligation to prove my open-mindedness to anyone.

I would read it after he walks on water.

I greatly dislike people who try to pressure me into something with a so-called challenge. The truth is, I read what interests me and not because of pressuring in the guise of a challenge. That is disingenuous and a turn off. Idk about others and I don’t feel a need for approval from anyone. If you tell me what you like about it and why , I am open to listening to you. When people pull that stuff, I see it as a form of bullying.

Good counter move.

I once got someone to read "Christianity, Social Tolerance and Homosexuality" by John Boswell, but beign a college level text and their narrow viewpoint and understanding, they couldnt' "get it." mostly because he assumed that what hsi church told him was true, and he had been conditioned (or taught) to not actually think for himself.

Neither book seems like a page turner.

I just checked out the rating on Goodreads. It has 4.18 out of 5 stars. I linked to the page if you want to peruse the reviews

[goodreads.com] ​​

I've not been "challenged" to read it. However, if I were, I'd ask if the challenger has read the entire bible, Old and New Testaments, from cover to cover? I'm not taking their bait. They don't have a leg to stand upon.

Haven't been challenged, but see there are plenty of criticism's of the book available. One I just finished skimming seems to do a reasonable job: [trollingwithlogic.com]

A lot of Christian colleges require that book to be included in a syllabus.
It is, unfortunately, the best they can do without no including evidences and critical thinking that would undo most of their own arguments.