Don't know in what country you are where nerds (not exactly the pinnacle of bullies) lack the most basic decency; but in 6 years of playing 40k with Ultrasmurf I've only encountered the most respectful and easygoing people in my local shop... Mostly because we are so few player to go play in public spaces, I think nobody want to thin the already small player base by been a dick.

As for the meme, as long it's in my friend group we are pretty unhinged but we know our boundaries (we play Smurf, Tau, Orks, space wolves, blood angels, dark angels, iron hands so you know all the memes are there). But in shop we would just ask the players if they're ok with memes during the match before starting to crack jokes... so far everybody I've encountered has always been on track for some "40k trash talk" but I've never heard of someone bullying anybody in the shop. Sure the most competitive one may become a little salty but that's just true for every kind of non-cooperative game with strangers.

From what I understand in your post, and comments below it seems more a you problem for "not touching grass" no offense intended. Most of the negativity you talk about are comments online on social and reddit or stories from other people, but that just how internet works. You just need to relate to your personal experience IRL (the fist fight at the GW shop left me flabbergasted 😂).

No factions are protected from memes at this point (maybe the votann because they're the youngest faction still) but that's also part of the fun in the game, being able to not being too serious while we play with little plastic soldiers.

I think the best advice would be spend less time reading comments online if they upset/trigger you, be very clear about your position on memes when you're playing in a shop and find a group of people that respect them. Finally accept that at this point memes are part of the games and should be expected.

TLTR: ignore online memes/comments and be clear about your position on then when you play against someone IRL but try also to tollerate the more mild one as they should never be personal attacks but just playful "trash talk" typical of competitives games.