If you roll 100 in either a need roll or a greed roll, you’ll get an achievement. And this often happens in a dungeon, where several persons want the same item.
But if you’re not doing an endless run of dungeons, you can speed up things a bit and increase your chances of getting the achievement. This is totally legal, and you can even help your friends at the same time.
When you’re out there questing, just ask a friend to group with you. Your friend shouldn’t be near you for this to work.
Every time a green or blue item drops, you’ll get a dialogue box popping up, asking you to either need, greed, or pass on the loot.
As an extra bonus, if either of you is an enchanter, you can enchant loot on the fly, using this same trick of being grouped.