Ok, instead of making a normal group, simply make it a raid group...
Unless a quest is designated as a "Raid" quest in your quest log, you will not receive quest items (or credit for quest-related kills) while in a raid group. If you are in a raid, then quest items will not drop, and quest kills will not count.
Good way to get your friends and other people to just say what the !@#$%^&* when they can't do any of their quest stuff at all (not even picking up quest items that spawn in the open).... have fun
just plain mean, and kindof common sense, although it is kindof funny if you go and loot Ras Frostwhisper's human head and then quickly change it to a raid