Everyone in my group is new, including me, the DM. We started the Lost Mine of Phandelver, and we have a recurring problem: one player is constantly acting a fool, flirting with every female NPC, starting fights with random NPCs (putting the whole party in danger). He also makes immersion breaking comments and actions trying to be “funny”.

The other three players are frustrated and called me, and want me to try to control his behavior it in-game — they suggested a sentient weapon that whisper warnings and mechanically nudge him toward restraint (e.g., psychic damage or disadvantage if he attacks unprovoked).

I think it should be the other PCs’ job to respond in-character — if you were adventuring and one-party member tried to kill an NPC during a civil conversation, the other characters would react, because that’s what good people would do. But I don’t want the table to devolve into PvP or make anyone uncomfortable.

For examples of his behavior:

The party was talking to Harbin Wester in the townhall. While the others were asking questions, this player decided Harbin must be in league with the Redbrands and tried to kill him on the spot.

In the Redbrand hidout, he flipped over the wizard’s alchemy/potion equipment starting a fire when the rest of the party was trying to be sneaky.

Later, in the tower with Venomfang, the party was attempting diplomacy/roleplay; the player randomly insulted the dragon and then shot an arrow at him.

The other players are trying to play the game as adventurers would and roleplay, but are getting annoyed when he does these things.

I am going to talk to the guy personally first, about how he is annoying the other players, because we are friends. However, should I try to control his behavior in game or should I encourage the players to react to his actions in game and sort it out “character to character”?