I clearly state that I intend to roll on DPS-gear at the start of dungeons. I clearly state they're allowed to, as well.
If they mind, I'm free to leave. I have instant-queues, it's no worries for me.
There are so many incredibly spoiled plate-dps'ers already, and you always end up in group with them.
With that said, I usually greed anyway, if a dps-item drops, and someone needs.