Prepare yourself, because internecine is a gloomy word. It’s an adjective you’d use to describe a bloody battle where both sides are badly hurt. On a lighter note, it can also mean a conflict that tears an organization apart.
A combination of the Latin inter- ("among") and necare ("to kill"), internecine conflicts are full of blood and death, and they end up destroying everyone involved, which sounds fair but also awful. Many wars are internecine, as are most Shakespearean tragedies and Hollywood action films. An internecine meeting would be one where everyone gets mad, says really horrible things, and then suddenly leaves, plotting revenge. It’s probably the last meeting for that group, which might be a good thing.