When I'm in a group, before we even enter the flashpoint, I state clearly how I will loot so it doesn't come as a surprise. I need on stuff for my character, I greed for stuff on companions, pass on everything else. It seems to be the most courteous way of handling it, but you just have to go into groups knowing there's likely one selfish, inconsiderate, thoughtless d-bag who's going to not care about you. That's just the nature of the beast. Besides, if that happens, just need on every single solitary thing and when you win something he/she really wanted and complains about it, you can say, "Yep, now think about whatcha did."