Wearing a ring of conflict creates a scene of conflict around you, and so is one of the most useful but dangerous rings in the game.
Putting on this ring has several effects. Peaceful or tame monsters will start attacking you or other monsters near them, though for all other intents and purposes they are still peaceful/tame, e.g. attacking them still carries consequences. This makes wearing the ring dangerous near strong pets, shopkeepers, or other peacefuls. However, it will also make nearby monsters attack each other instead of you, which is incredibly helpful, especially in high-density areas like the Astral Plane and Moloch's Sanctum.
Specifically, monsters are affected if they are in your line of sight and at most 8 squares away. Blinded monsters and the Wizard are impervious to conflict. Monsters with a sufficiently high combined magic resistance and level can resist this.
Additionally, if you are generating conflict when you arrive on the Astral Plane, instead of getting a guardian angel you will be attacked by some hostile angels. If you aren't wearing the ring when you arrive, but later put it on and your guardian angel notices, it will also turn hostile. This ring also has another effect: Monsters will move around randomly if they engulf you. This ring can be very helpful, if used properly, to a pacifist.
Identifying a ring of conflict is easy. Just put on the (ideally noncursed) ring and see if any peacefuls attack you, or if monsters attack each other. A common YASD is to BUC test a ring as noncursed in a temple and immediately wear it; if it's conflict, chances are good the priest will obliterate you.
Dropping a ring of conflict into a sink produces the message, "You hear loud noises coming from the drain."
Unfortunately, wearing a ring of conflict burns nutrition very quickly: every even-numbered turn your nutrition is decremented.
If you are not wearing the ring, conflict can be toggled by invoking the Sceptre of Might. This has exactly the same effects as the ring, including attack level in resistance rolls, but will spare you from hunger.