In fact, it seems the only way to really avoid loot drama is to, unfortunately, be as selfless as possible. Last night, I did a run of Ramparts on my up-and-coming hunter, and on the first boss, the Hunter mail pants dropped. The other Hunter in the party needed them as well, so we rolled on them, and I won. Later in the instance, another green piece came up that we both needed, but to be fair, I let him have it. And finally, on the second boss, the mail hands dropped, and I did need them, but once again, to avoid drama, I just let the other Hunter have them. I could probably have made a case for at least rolling on them, but it wouldn't have been fair for me to walk away from the instance with two blues when he only had a green, so to keep the peace I let it go.
It worked out, too, because I picked up some great blue hands anyway when I turned the quest in. And that's the thing to remember when it comes to loot -- there will always be more of it. Even if your item doesn't drop, or you don't win this roll, or your guildie gets angry because you nabbed an item, even though they knew you needed it, there'll always be more drops and more rolls and more loot to get.