To add to what Dark Trainer said- if you are WAAC/Competitive Player and ROFL Stomp a casual player, don't pick apart their entire list, or tell them how they could have played better, or what their mistakes are unless they ask or seem inclined to want to know. All you are doing is trying to make them into a WAAC player. "You could have won if you had brought the Succubus instead of that in your list. On turn 1, you should have shot at this unit, not that unit. Why didn't you bring this unit instead of that unit? Don't you know about X,Y and Z combo with this strategem? Player X won World Champion GT with this list."
Casual players don't want to hear ANY of that. If you just kicked them in the teeth, shake their hand, say "Thank you for the game" and that's it. Walk away. Telling such a player how they lost, that they should have taken A,B,C units, that they should have done this or that... that's like kicking them when they are laying on the ground bleeding from the savage stomping you just gave them. If they don't ask, don't offer.
There needs to be a social contract between the players before a game. "I'm here to play a game and have fun. I want to roll a lot of dice, I want to laugh, I want to cry, and I don't care if I win or lose. It's how I want to play the game. If you don't like that idea, then let's play a different game or find new opponents."
During a game, if you look across the table feeling great with a big [big bad swear word] eating grin on your face and your opponent looks upset, bored, disinterested- basically everything you are not feeling, ask yourself why, and what you can do to make them feel better or have a more fun game. In other words, show some empathy towards what your opponent is feeling. Don't just shrug your shoulders and keep on playing.
I'm reminded of X-Wing Worlds back in... 2015 I think? I wasn't a very good X-wing player. I just brought what I wanted to play. Somehow, in round two, I played the guy who would become the winner of the whole tournament. I was having fun. Moving my ships around in unexpected ways, taking long shots with little chance of hitting, and about half way through the game, he threw a huge fit. He accused me of sand bagging, being intentionally difficult to play against, cheating, and trying to time out. We only had about 15 minutes left in the round and by some miracle, I was ahead in the game. X-Wing had just introduced the T-70 X-Wing that had a Tallon Roll maneuver that was new to me- I'd never used it before and when I finally did, he exploded on me. I was a bit shocked- he started shouting at me and I totally thought he was going to flip the table! Judge comes over because the guy was screaming at me. I explained that I misunderstood how Tallon Rolls were performed, and that I did not know I was being a difficult opponent. I offered my hand to my opponent and said "It's OK, you win. I concede. You are way more invested into this game then I am. I'm just here to have fun." He refused to shake my hand, and I packed up my ships and dropped out of the tournament. The Judge as I was leaving said "Hey, you would have won, you don't have to leave. That guy was just a poor sport." I said to the Judge "It was more important to him that he win then for me, so I let him win." and I shrugged my shoulders and that was that. The Judge did offer me some alternate artwork cards and Worlds template, but I told him to give them to the last place guy. I was done with X-wing. Played maybe a handful of games after that before selling it all off. One guy had destroyed any kind of enjoyment or interest I had in X-wing.
Games workshop feels VERY strongly about this. So strongly that they devoted an entire page of 3rd ed AoS to it, and it's not ambiguous at all. It clearly states how you should act. It's important enough that it's reprinted in the 2021 General's Handbook for Pitched Battles. I expect the 10th ed 40K rule book will have something similar. Right now, it's scattered all over the Core Book in the sections few, if any players read.
Other companies have done the same. Privateer Press had a very controversial "Page 3" for the longest time. Players took it as an excuse to WAAC and be jerks while playing the game. PP stopped doing the Page 3, and instead devoted a lengthy page on player etiquette and sportsmanship in their Steamroller Tournament document. Those of us that remember playing in the GW Grand Tournament's of the 90's will remember the 2-3 pages devoted to sportsmanship during the GT. The Atomic Mass Games/Fantasy Flight Games (Marvel Crisis Protocol, Star Wars X-Wing, Legion, and Armada) all have sections about sportsmanship. I'm hard pressed to think about any tabletop game that doesn't have some kind of section about sportsmanship or "casual vs. competitive play".
Sorry Lyraeus. You seem to equate winning as fun, and you don't understand why players don't try their hardest to win. The old quote here is probably the best thing I can say: "It's not whether you win or lose; it's how you play the game" - Grantland Rice. You play the game to win. You equate that with always trying your hardest to win. Bring the hardest lists, the most powerful combo's, etc. etc.
TLDR; Get off your winning is everything high horse. Your entire post comes off to me as "I'm better then casual players because I play to win and I don't understand why you don't".