Can't really fault the Kurloz roleplayer for asking about Prince of Rage, though it does seem like you should already know this? :p

Prince(ss): Someone who destroys their aspect outright. They are at odds with their aspect, and usually even destroy their aspect within themselves. It’s also shown that they destroy their aspect so that it can be rebuilt stronger than it was before. (It is my own personal speculation, so feel free to take this or leave it, that a prince's ultimate challenge is to rebuild their aspect within themselves after they’ve destroyed it).

Rage: Insanity, chaos, destruction, obsession/conviction, and negative emotions with a huge focus on anger. Associated with physical strength, many rage classes would be brawlers in an rpg. They reach their full potential when pushed to their mental limit and/or under an extreme amount of stress.

So Kurloz is honestly a pretty strange one. Been a while since I've played openbound so I went ahead and thoroughly read his wiki page. It seems to be that him being at odds with his aspect comes from the specific incident that caused Meulin to go deaf, where they were both asleep together before he woke up from a nightmare and yelled or screamed (or honked?) loud enough to permanently destroy her hearing. The most explicit use of his Prince of Rage abilities come from the fact that he completely pacified her afterwards. Not only is Meulin not angry at him for it but she seems completely at peace with the circumstances and enjoys learning different ways to communicate. He also seems to take advantage of his ability to pacify her in order for her to not be alarmed at all by the instances where he possesses her with chucklevoodoos. She questions it but never seems to be able to muster any genuine negative emotions and just finds ways to write the weird instances off.

He did feel extremely upset over disabling Meulin though. His rage manifested as a scream, and so he destroyed that rage within him by taking a vow of silence and biting his tongue off. He still rebuilt his aspect within himself through going deeper into his religious convictions, which were most certainly insane and revolved around the concept of every single ghost in the furthest ring being destroyed through dying a double death.

Aside from that, the only other ways he could have possibly fulfilled his role as a Prince of Rage are speculative. The incident involving Mituna overusing his powers to save the alpha trolls from certain doom is shrouded in mystery, but Kurloz was indeed there. Mituna can't give a proper account of this due to trauma, but Kurloz for some reason or another just hasn't elaborated on what he saw. It's a personal theory of mine that after Mituna overexerted himself, that Kurloz was there to pacify Mituna after the incident was over, and may have even destroyed the memories of it from his mind. He may have also tried to help Mituna with whatever the threat was, fulfilling his Prince of Rage role by trying to destroy whatever it was that threatened to destroy them.