I never finished an RP, although I did complete a character's arc in an RP over the course of like 4 or 5 years one time. That was probably the best (and also one of the hardest) things I've done in an RP before because killing off someone who's head you've lived inside for about a quarter of your life (at the time) isn't fun and I still miss writing as that character to this day.

However it was a great experience to take a character to their logical conclusion. They were always one of those more unstable asshole-ish characters that had trouble getting on with others in the group, and it was established during the narrative they were slowly sinking into a feral state as a result of degenerative disease (this was part of the main RP plot incidentally, not my down device). It was really sad because there would be periods where they would kind of warm to the others, then there would be some perceived slight or betrayal that would set them off and push them further away, and this built and built until my character ended up trying to kill the leader of our group. He loses, and is killed.

The thing that was so great about it was that it forced the group leader to also deal with a bunch of stuff and evolve and change as a leader, as well as completing my character's spiral into self-destruction. But still, all very bittersweet. I don't write as that character anywhere anymore because it doesn't feel right. I finished their story. Sometimes I would have liked to give them a different ending, because looking back there was a fair amount of me in there in many ways, but its never felt right.

Yeah so that's probably the best moment I ever RPed, the death of my favourite character.

There was a lot of stupid stuff as well, like the time me and friend got bored of a survival RP so spent a night whole replying to each other to build up an elaborate suicide pact death scene. Or one time a high school RP we were in died except for me and the same friend, so we highjacked it and introduced some Lovecraftian demonic characters we used to 1x1 with to slaughter everyone else. That was fun, but the best moment was still probably killing off Rolnak.