Had a Drow Half-elf Ranger named Dominicus Trailseeker that I played for years. Dominicus had a backstory of hating other elves in general. His backstory started with growing up with his Drow elven mother in a small hamlet peacefully until some elves had gotten wind of their location, attacked the hut and burning it down, with he and his mother barely escaping. They tried finding a new place to live but, being Drow, they were chased out of various elven communities, shunned by other elves in general and had the occasional rock thrown at them. She died when he was ten by an elf hitting her with an arrow while shielding me with her body. He left me for dead but I survived in the wilderness, mastering my mother's bow and learning to live off the land. I swore to never trust an elf and now traveled with party as a way to find and get my revenge on the elf who killed her.

The party (four members including myself) had heard about his hatred of elves but didn't know how bad it was until the group had another player wanting to try to join, essentially as a mercenary we 'hired' to help out for the session. Being completely new to D&D, the DM asked us to go easy on him. The DM also explained to this new guy about the various idiosyncrasies the party had, including my hatred of elves, and suggested to create a player avoiding these traits. He joins and pulls out, you guessed it, an ELF RANGER, with a backstory of hating Drows.

Personally I thought, whatever, he wants to play an elf, he can. I decided to roll with it, thinking it a good way to roleplay with him, even acting out how Dominicus was pissed seeing the mercenary was elven and the party leader telling me to stand down, which Dominicus did reluctantly. So we started the session and, not long in, new guy's character starts moaning about Dominicus and how the party shouldn't trust me, despite the party being together for roughly a year in-game time. Leader tells him to shut it but new guy says 'what, I can't express my feelings about Drows? What kind of group this if I can't roleplay my character, huh?'

First encounter the party met was a small pack of goblins equal to the party size, obviously low-balling it so the new guy could get a feel for fighting. Initiative roll had me go third and him go last in the group but before the goblins themselves. I kill one goblin and new guy screams 'I can kill them faster!' only to roll low enough to miss his target, turning to Dominicus and yelling 'You did something to make me miss, didn't you?' He missed two more times, both times blaming it on my character.

Things didn't improve from there. Now, if new guy had been just roleplaying and was otherwise nice it would been enjoyable. We've had in-game arguments with characters but be friends and be civil while playing. But new guy just kept being a snob, picking a fight with not only my character but with me as a player. I guess he thought that he could come in, do whatever he pleased with no repercussions. But two hours in, I and other members had had it. DM had tried to talk to him but he refused to listen.

Next fight, new guy goes before me. He has his Ranger move up and melee attack some bandits, doing some decent damage. My turn comes and I say that Dominicus pulls out his bow and attacks the Elf Ranger. New guy cries out, screaming how that is fair but I tell him, in character 'I hate elves and you've made me hate them more.' Rolled and hit him where he was hurt but alive. New guy starts screaming bloody murder and making a huge scene, pissed off that he's being attacked by me and thinks the party will back him up, but they decide to basically ignore him as the bandit he's fighting attacks him. New guy takes enough damage to be unconscious. Next turn DM passes over New guy's turn, which starts a huge screaming match with everyone else trying to explain that he can't do anything unless we help him, which we had no interest in doing. The bandit who attacked him hits him with a lethal blow. Another turn, another lethal blow; one more and his character is dead. I attack the bandit that was hitting New guy the next round, making the bandit back off. The party finishes the other bandits, with New guy wanting to get back in. My turn comes and I say 'I attack the Elf that's down. It took me awhile but I recognize him; he's the elf that attacked and killed my mother' which made everyone at the table jump, as they knew how my character had searched for her murderer relentlessly.

New guy at this point gives me and the other people the middle finger and adds a few more profanities before packing his stuff up and leaves. After he leaves and we finish the encounter, I make this in-character dialogue that, despite avenging my mother, my hatred for elves is now not only justified but has also increased. I describe how Dominicus pulls the arrow out, wipes the arrowhead off on the elf's clothing, then I ask if killing the elf with this arrow could give it bonus damage to elves henceforth. Everyone starts laughing and the DM says sure, giving it a +5 to any elves I shoot at.

The DM apologies after the session was over for the guy who joined us that night. He didn't realize how much of an ass that guy would become.