My pick would be, dealing with the ‘wild west’ atmosphere. That being, before cyber bullying laws existed, you had bunches of people getting off scot-free with telling you to off yourself or call you a list of derogatory terms.
You’ll pry “Slime Volleyball” away from my cold, dead, fingers. Also Minecraft, which I believe was as Java applet first. Also Robocode.
So many good Java things in that old web…