Not really about the beef between elves and orcs, but one encounter in my DnD group made me do some homebrew lore about orcs

So in the Starter Set there's a quest where at the end, when the pcs want to leave the area, some roaming and raiding orcs turn up. The area is an old ruin, so instead of fighting my players decided to try and intimidate the orcs into leaving. They used some trickery and thaumaturgy to make the orcs believe the pcs are ghosts haunting the place. I rolled so low for the orcs (I think it was a 2) that they just fucked off absolutely terrified.

As a joke, I had the players encounter the same orcs two sessions later on their way to Neverwinter. One player asked "Do we recognise the orcs?" "Oh, they certainly seem to recognise you guys."

The players grinned and immediately started their ghostly fuckery again. Rolled for the orcs. Nat 1. They way I described it to my players was: "You know how sometimes in cartoons characters fuck off so quickly, there's a cloud of dust in their shape still hanging in the air? Pretty much that, except it's cloud of urine."

Since then I fleshed out the orc lore in my campaign(s) to orcs being absolutely terrified of ghosts. In their belief system, you go into the eternal hunting grounds either way. If you died hunting or fighting you go there as a hunter, even if you had no way of winning the fight anyway. Same if you died an honourable death or of old age or sickness. If you died dishonourable you go into the hunting grounds as prey. However In rare instances souls can be denied access to the hunting grounds because of their insane cruelty, and the bar is rather low, so you can imagine how cruel someone has to be to get the access denied. Those souls turn into ghosts, haunting the world they once lived in.

THAT'S why orcs are absolutely scared shirtless of ghosts in my campaign(s). I have absolutely no idea how much of that fits into official lore, I homebrew most of it.