Ness v Butter refers to the war between members KirbyIsNess and Butter.
Ness v Butter started off after KirbySSM, the owner of the server, created a M$ Paint drawing of KirbyIsNess holding KirbySSM at gunpoint. This, among other things, caused KirbySSM and Butter to tag team on ness, claiming he is texan. Eventually they came to an agreement for Ness to write a paragraph in the lore channel and that ended this fight. This did not end things for butter though, who continued to fight with ness.
The War essentially was a conflict between Butter and Ness. Butter had usually jokingly made mean remarks and critiqued Ness for many things, and Ness seemed to take it as a personal attack.