I only Need on gear/items I will will personally use/equip. If it's something BoE for another character of mine, I ask the group if I can Need it and I'm fine if they say no.
In any case a firm policy needs to be stated at the beginning of the run and if you are not fine with that, leave the group (it's better than being labeled a "loot ninja").
I am so tired of people who Need on everything with the reason of:
"Everybody clicks Need all the time so I'm just protecting myself from getting cheated out of my fair share" (well they sure will if they ever get in a group with you again!). Sometimes they also throw in a dig about how if you say you don't Need all the time you are lying or naive/a newb.
"I can sell it to a vendor/post it on the exchange so I do Need it" (this is especially odious when Needing on BoP gear worse than what you already have or that you cannot even use (like a Tac Needing on a Science kit))
"Oops my finger slipped" (for the eleventh time...)
(In WoW Enchanters were the worst in PUGs, "I can disenchant it, so I can "use" everything we find..." <boot><ignore>.)