(Guy's preamble: This was originally posted on my ask.fm, where a Fate/Stay Night fan asked what sort of behaviour I'm anticipating from F/SN fans that'd impact the fun out of non-fans' viewing. I edited some of the specific references out or added others. And sad to say, all these things I predicted did indeed come to pass, and with double the vigor once full series/cour reviews had come out by people who were not True Fans. Of course, this is relevant in any season where a popular franchise is adapted, which is basically every season. I'd like to reiterate that this behaviour is understandable, and even I sometimes engage in it, but as always, we can strive to do better, especially if in our zeal to convince people to love our favourite shows as much as we do, we rob them of the opportunity to engage in it as we had.)
A lot of it is down to the same sort of behaviour that is prevalent when any adaptation comes out, or when people read/view one part of an interconnected universe, or even when people read the first part of a series you've read the entirety of. It just happens that the more "hoops" you have to jump through in a specific work (in terms of word-count, how many interconnected series there are, etc.), or rather, how artificially high the barrier of entry to "true fandom" is, the more this behaviour is prevalent.

So, what to do or not do, right?
Don't give spoilers. Don't tell, "You think X was cool? Just wait till next episode!" or when someone makes a prediction, don't go, "Ho! Just you wait...." and that sort of stuff. It's not actually fun, and ruins the fun of trying to predict stuff. That's actually one of the highlights of consuming material where not everything is spelled out from the get-go, and what spoilers, even "hinty spoilers" rob people of, rather than the "story-beats".
Don't tell us we don't understand stuff because we hadn't read or watched this half-dozen related sub-series taking place in the same world in order to explain the in-world logic to us. The show needs to stand on its own, in your attempts to defend it, explain stuff to us, you're sucking the fun of actually watching the anime adaptation. The series fails to explain something that can only be understood if you're willing to pour 50 more hours into the world? That's a failure of the work, pointing it out will not erase it, but only reaffirm it.
"The original material did it better." "I was disappointed by seeing how they chose to handle X compared to that scene in the original material." - First, a disclaimer that's important for all of these, replying to one person who compares to the original material with this is cool, starting your own discussion where you do it is cool, replying to someone who's only interested in the adaptation, isn't. This is the biggest point fans of original material don't get - when people keep saying what you're watching is shit, they don't make it more fun to watch it. "The original material is better" is an attempt to get people to give the original material a shot, which is usually going to fail - if I think this is shit, why would I watch the original material? Fans of a series are also not a trustworthy source.
Another thing "The original material is better" often is, is an attempt to deflect criticism of the series. With Mahouka, I can personally attest a lot of times that people brought it up, but the exact same issues existed in the original material as well. Furthermore, it's just shutting down discussion of the adaptation.
Here's the thing to keep in mind - we can all read/watch those other series/content. We chose to view this. So treat it as a work that has to stand on its own, and stop comparing it to other stuff, and stop spoiling this, and spoiling other stuff in order to explain this material. So, Tsukihime (or The Silmarillion) explains Kara no Kyoukai (or Lord of the Rings)? Cool, but why are you spoiling Tsukihime in order to belabour and suck the fun out of Kara no Kyoukai for me now, while also ruining my enjoyment of Tsukihime in the future?
The simplest thing is, if you're a die-hard fan, don't actually engage with the anime-only watchers, take a step back, let them have their fun, and limit yourself to discussing with other die-hard fans.
Let's try to make it productive: How do you engage with people who are watching something you care for deeply, while not annoying them overmuch, or shaping their viewing? Or perhaps you wish to shape their viewing The Correct Way™?
All the images in this post were made for promotional purposes and/or fall under the jurisdiction of fair use. The image used in this post is from the anime Gekkan Shoujo Nozaki-kun / The Monthly Nozaki-kun.
This post has originally been posted on my blog here, and has been reformatted and updated as needed for Steemit. You can verify I am the blog owner by scrolling to the bottom of the right sidebar.