It took me a bit of time to think of a good answer for this, but here goes.

Back when I was relatively new to the game (and had just started going by the name Black Ninja), I played in the Battle Server a lot. On occasion, I would (like everyone else did at the time) roast The Server. One day, I saw The Server sitting in the upper-left corner of Diamondus Warzone. I hopped up there, started to blast him, and then, something odd happened. Much to my surprise, The Server came to life and destroyed me utterly.

Best JJ2 moment ever.