Ran into a situation last night where we had a pretty well-organized server but missed out on gold reward several times due to a griefer. The fellow would gather up as many veteran adds as he could manage and lead them right into a team, usually Boom-Boom. This would cause a team wipe, or at least a partial, and push just that one boss into silver time limit. This individual was clearly griefing, but he did chant “I’m going for the achieve!” repeatedly. Here’s the PSA part.
Organized players: DO NOT FEED THE TROLL. If you run into this, I find it is easiest and most effective for a GS Guardian (in this case, myself) to #5 and counter-pull the mob away when you see them coming. It ends up being a self sacrifice (unless you can handle 10+ vets) but saves the team, and is much more efficient than just yelling at the griefer.
Newer players: THIS IS NOT AN ACCEPTABLE METHOD FOR FARMING ACHIEVEMENTS. Some of you may think or may have been told that it’s easiest to pull mobs into a group of players to kill them faster and get the achievements faster, but you’re only damaging the event and ruining the experience for others if you do this. There are usually groups in between events killing mobs, as well as the occasional server in LFG that focuses exclusively on mob farming. You can find willing help, so please seek it instead of taking advantage. We’d all love to play in harmony here.
Trolls: Well, not much point in even addressing you guys.
Hope this helps!
I have a “band”, Beatiatrician:
http://youtu.be/zw_Sl-El8_I 
I’ve always seen groups advertising achievement farms, but maybe I’m just lucky lol.