This seems a good a place as any to ask this...
I just recently started playing lots of games (on roll20) with various DMs. Before this point I had played only with a handful of other people, over a period of several years, and aside from that I've DM'd a campaign for a long time. I have a pretty good grasp of the rules, I think, even though my 5th edition binge just started a few months ago.
I like to know rules. If I want to accomplish a task (or one of my players does), I like to know how the rules say to do it and I'll try to accomplish it using existing rules before I start making up my own stuff. Something I'm starting to notice is other DMs and players don't seem to know (or use) the rules as well as I do. Like, not nearly as well. They'll say something about making a grapple using an unarmed attack, or not being able to use my mount's action to Disengage, then use its full movement, and use my own action to Attack, and I'm a little flabbergasted because I know that's not right, but at the same time I don't want to be that guy who always tries to tell the DM how to run their game.
What's the etiquette here? I don't want to be a "rules lawyer", as it's generally something used in a negative context, but if the DM says something like "you had a random encounter during your long rest, now you don't get the benefit of the long rest", should I be pointing out that the long rest rules specifically say you'd need to be fighting for at minimum 1 hour for our long rest to be interrupted, and a typical encounter is less than a minute? In some situations I imagine DMs are just houseruling things they don't like, but there are also times when I just feel that the DM is genuinely ignorant of the rules (or using the rules for an interaction that were right in a previous edition but are not right in this one).
I suppose part of the problem is that these aren't people I know terribly well, given we're playing over roll20 and I'm "the newbie". But what's the best way to bring these issues up to a DM, as a player? Or should I just be "rolling with the punches", as it were? Maybe other DMs would like to tell me how they'd like players to bring such issues up--because if I were a DM, I would want my players to point out whenever I make a rules-related slip-up. But then there is that negative stigmata of "rules lawyers" which makes me think that others don't feel comfortable being "undermined" as it were by their own players.