catalog sue

A variation of Mary Sue, this character uses the most OP item or item combo they can instantly get their hands on at the expense of the metagame and/or other players.

The name derives from the Roblox game Catalog Heaven.
They differ from munchkins due to how they appear and their needed time: Munchkins arrive from the idea of OP characters and usually take a few hours in order for their avatars to become a problem, whereas catalog sues arrive from the idea of easy kills and become a problem as soon as they get on the battlefield.
The main problem with them is that they create a constant cycle of increasing players, regardless of whether or not other players approve of their actions: When a player sees one them and gets into the idea of a large kill count, they will start using the same items to reach those same numbers. When a player sees one of them and despises their actions, they may use similar or stronger weapons in order to take them down. Both result in more players seeing the use of such weapons and continue the cycle.
Because the only way to counter a catalog sue in to use similar items (thereby adding fuel to the fire), your best option is to simply avoid them. Fewer players around them means fewer kills, which makes them more likely to consider their actions or leave the server. Talking to them may also help.
Remember, when everyone has a equal chance to come out on top, everyone wins.