Yes, I agree it's annoying for amateurs to think they know more than you. I knew a fellow once who, having read the books, was a little snobbish about it, and kind of sniffing at the movies and saying they weren't entirely true to the books. Then he came up with some crazy idea that Tom Bombadil sent the Ents to Helm's Deep. I was like "uh...NO?" and he didn't agree.
I suppose I would suggest, however, that we as Tolkien fans (as representatives of Tolkien fans) take care not to appear intellectually snobbish back, and act like a know-it-all in return. (Not saying anyone's doing this...just suggesting we keep it in mind when dealing with people who are probably pining after all our superior Tolkien knowledge!)
Try playing Lord of the Rings Trivial Pursuits with them. This is both helpful and revenge, since it will assist them in learning about LotR, but until they learn their stuff, you can totally cream them.
