I'm directing a 5e campaign and I have a party of three: A Tiefling Warlock (eloquent, rational type), a tiefling monk (rash, impulsive and danger seeking) and a half-elf rogue (his personality is not that well defined). We're all adults: I'm 26, the warlock and the rogue are 25, and the monk is 29.
I had this devil trapped inside a magic circle, and a puzzle involving a talking severed head and riddles. As a reward for freeing him, the devil drops three rings (one blue steel, one red iron and one orange copper) to the floor and says "Pick one", before disappearing.
The three stare at the rings, and the monk (who solved the riddle) said: "I will take the blue one first, you can get the others if they are still there."
The warlock was silent, staring at the rings and thinking.
The rogue asked the warlock to identify the rings before touching them (not possible).
When the monk heard that the warlock could not identify the rings he said "I reach for the blue one and I take it!" The other players did not react and I rushed to say, "The other two rings dissapeared!"
And then it all broke down. The player who plays the rogue wants to stop the monk from touching the rings. I make them do a dex throw and the rogue won. But I had already said the rings disappeared, so in order to keep the narrative going and not allow them to meta-game with the knowledge, I ruled that the rogue was able to stop the monk from taking the ring, but he touched it with a finger and the other two disappeared.
The rogue starts complaining, claiming its not fair, and gets mad (the player). He takes it personally and starts to put away his things, really angry. I told him I already said the rings disappeared, and I'm not getting them back, and that I already gave him the chance to fight for the remaining ring, even though he has been getting all the magic items lately, and the monk has nothing yet.
He says he wants me to pause before narrating the consequences of the players actions and ask everybody if they want to do something, so that everyone can react to everything. He starts making threats, saying he cant play with us if we can't play like he wants.
And when I explain to him that he has to roleplay that anger in-character, against the monk, he says "from now on my character is going to do the opposite of what the monk does and wants. And if he does something like this again, I'm killing him, and it's not my fault because I warned him".
It took me a while to get him to calm down a little, but the session ended a bit on the cold side.
For the record, the other two players side with me, and agree that events should flow naturally, even when it's not totally fair to the players.
What do you think? I don't like this behavior, and being called unfair touches a sensitive string, because its been multiple times now that I've done things to keep this player happy, including talking to other players individually and telling them to tone down their arguments with him and giving him a good amount of the loot and letting him get away with some power-gamey stunts.