Dungeon Finder achievements

I was doing a random heroic today for my daily two frost badges, and the other 2 dps and healer were from the same guild. Before the final boss in Halls of Stone, one of the people in the guild suggested we try Abuse the Ooze achievement, which requires fairly high DPS. The problem was one of the guys from the guild was clearly an alt or a new 80 in mainly blue gear doing less DPS than the tank. I didn't feel like we had the dps for it, and didn't want to waste my time & money on an achievement I already have. I was polite, but the healer said "fine we won't do it, but I'm not healing you through the boss fight either". People really need to realise holding PuGs to ransom is pathetic, if you want an achievement make a group for it, or do it with your own guild. Don't expect people to go out of their way for you.