Once had someone like that very blatantly 'afk' in Labyrinth of the Ancients.

At first they just stood afk in the corner of the starting platform. When I mentioned them being afk, they suddenly showed up for the next boss - now standing around in the fight, not doing a single attack or using any skill. Sometimes saw them walking a bit, but not doing anything else.
Like.. why? Don't queue if you're not going to play. They kept doing that through two bosses, then someone in the party started a vote kick and the player got kicked. I didn't cause I was worried with the new TOS about harrassment that kicking a player for not using skills could be reportable (for the person initiating the kick).