Was this a RuneScape private server (RSPS)? I remember back in the day you could find a free RSPS DDoS tool with a quick Google search, and all you had to do was enter the public IP address to start attacking. The culture for the RSPS scene was exactly what you're describing.

Also there was another kind of attack where you would start thousands of bot clients at once that would spam messages. The hopes would be that you would (a) shut down the server, (b) attract the players to the server your bots were advertising