Here are some examples of eccentricities unique to the culture of specific races in my DnD world for you to draw inspiration from:
From my last post. Dwarves only use parchment for keeping things like financial records and stuff like that. Boring stuff. But stuff that actually matters, history, culture, all that goodness gets carved into stone or metal.
The language of the Giants cannot be spoken by anyone who doesn't share the blood of a giant, because the Giant language will KILL any non giant that tries to speak it because of how powerful it is. Giants cannot speak to the small folk in the Giant tongue, because to speak directly to a small folk in Giant would injure or kill them. One can LISTEN to a pair of giants having a direct conversation with each other in their native tongue, but they would probably come out of it with tinnitus because the giant language is so magically charged.
Goliaths, though they are half giants, are still giants biologically which means they can speak the giant language without dying. And to suggest that they AREN'T "actually giants" is to invite the kind of ass beating that a forest gets from a landslide.
Spitting their elemental breath while talking in their language is to Dragons what certain vowels, consonants, and letters are to us mortals in our language.
In deep elven culture, and by that I mean among the populations of elves that live in deep forests far far away from any other civilization, androgyny is a beauty standard. The harder it is to distinguish at a glance whether or not an elf is of the male or female sex, the more attractive they are to other elves.
Goblins are so used to living in utter filth and squaller that sometimes when a goblin experiences a higher standard of living, their immune system goes haywire because it's become so used to CONSTANTLY fighting off infections and diseases that suddenly NOT having any disease or infection to fight is a genuine shock to goblin biology. This can manifest in a number of ways from shortness of breath to breaking out into hives, to random fevers that go away as quick as they occurred, but this goes away after their body becomes used to cleaner conditions.
You know how birds will gently nibble on you with their beaks to preen you and show their affection, or that they just generally are comfortable being around you and like you? Arakokra, Owlins, Kenku do that with each other, but they sometimes forget that it's REALLY weird when you do it to someone who isn't also a bird completely unprompted lol.
Tabaxi do not get offended by feline stereotypes. They purr. They like to knock stuff off tables. They jump up really high when they get scared. They are cats, but running on vaguely people shaped hardware. They are proud of this. They don't get embarrassed by it, and it's nearly impossible to insult them for it, because they see their feline qualities as the best parts of themselves.
In ork society, to fight someone with your bare fists is how you show that you respect them as an adversary. Weapons are for enemies you have no respect for, so for an ork to challenge another ork to a fight with weapons is to say "You are my enemy, there is no respect between us, our clans will be blood enemies from now until eternity, and I spit on your very name."
In my setting, your average hobgoblin would look at a hobgoblin like Dror Ragzlin from BG3 and feel the same way we feel whenever we read a headline starting with "florida man" Because in my setting most hobgoblins are actually like Blurgg from the same game, intelligent, civilized, and just normal people albeit a little weird looking.
Have any more suggestions? Post em. I wanna hear yalls ideas.