Easiest way to turn off QM on a party member is to say in party chat to have party leader turn it off so everyone can lot on the items, especially if other party members didn't notice it WAS on or what that dot meant.
If they haven't turned it off by near the middle or end of fight, then just have everyone log off from the party mid-fight so the leader dies and no one gets any drops. Then never use that person again for a fight and make sure (via /yell?) that everyone else knows this person is a user/leech, too.
We had (notice past tense there) a few players on Asura back in the day that did this in Dynamis and Abyssea runs, and after they were publicly announced, they either left server, left game, or were never a party leader again.