Definition of "griefer"

First, be a tree; in other words, ignore the griefer. This approach can be very effective because most griefers want you to get pissed off, and if you don't, they may move on to more fertile targets.

2007, Brian A. White, Second Life: A Guide to Your Virtual World, Que Publishing

Julian Dibbell's description of griefer culture demonstrates a high degree of congruence with Huizinga's description of the spoilsport. The griefers have indeed “made a new community,” loosely organized on somethingawful.com and the /b/ forum of 4chan.org

2011, Kristie Miller, Marlene Clark, Dating: Philosophy for Everyone, John Wiley & Sons

“ […] Maybe we can set up a trap for the griefer.” “That's an amazing idea!” said Kyra. “ What type of trap?” asked Steve. “We can create something very valuable that the griefer might want to steal or destroy and we can wait by it until the griefer arrives.

2015, Winter Morgan, The Mystery of the Griefer's Mark: An Unofficial Gamer's Novel, Simon and Schuster