Hmm, lots of things to pick from...
Back when I first started playing the game, I was fighting gnolls on the top floor of Blackburrow. I had the misfortune of learning that the tree next to the Qeynos Hills zone line has a false floor and fell into its trap for my first time. I started walking around, trying to figure out where I was, but I had never been that deep inside of Blackburrow before, and eventually, I found death.
I didn't know what to do. I had lost all my precious gear, and I had no clue how to retrieve my corpse, and then all of a sudden, I received a tell from a level 16 barbarian shaman saying they see my corpse. They asked me to /consent them and said they would bring it up top for me.
I was so relieved. The shaman and I got to know each other pretty well over the next few years, and we even met up in person. He moved onto other games, such as World of Warcraft, but we still keep in touch here and there.
Quite an experience going from meeting someone in the game to becoming friends in real life.