A resent experience I had which as left me wondering if I should take a break from DDO while the players grow up or more mature players join DDO (I have already decided not to spend the $50 for the preview) led to another thought. With players having the ability to start at level 15 now if someone wanted to get back at another player it is now possible to create a level 10 or 12 or 15 toon (cleric comes to mind since they are usually always needed in a quest) the same level as whom ever you wish to mess with. Then when they post on LFM join the party and make sure you find ways to mess up the quest (don't heal the guy you are messing with/exit and re-enter/make sure the quest can't be completed (only works with a few quests)/etc. You will likely be ignored, but that doesn't matter since as soon as the quest is over/failed you will delete the toon and create another using a different name to do it again later that day or the next day.
I can only assume this will work since I don't (and don't expect to) have access the iconic toons.