As the one in my playgroup who understands the rules the best (Mostly from watching Magic Online, so I see how the stack works), how do I best go about explaining rules interactions to people when they want to do something and it doesn't work that way? It's usually something stack-related, so I can't just point to something obvious and say "This is that rule", but otherwise I sound like I'm just cheating for my own benefit. Is there any way to make it sound like I'm not just making things up?
The best way to accomplish what you’re trying to do is to educate. Try to explain the reason for the rules being the way they are. Use simpler language if they’re not understanding certain concepts. Think of a situation that would lead to a contradition or an unbreakable loop if the rules worked the way your friends think it should work.
For the stack specifically, you can actually build the stack with cards and paper. Write out triggered and activated abilities on pieces of paper, building a physical stack and showing how things work when going on the stack in APNAP order and resolving last in, first out.
