Last night I was playing with a random group of people on a suicide mission. I found the super samples and said in voice chat that I was going to drop them at extract. A few minutes later, a level 23 guy ran to extract and picked them up. I said in voice chat, "hey, can you drop those samples back on extract so we don't lose them if things get rough?"
No response. I figured he must not have voice chat turned on. Oh well, I'm sure we'll be fine. We start doing the rest of the mission and about 15 minutes later, I see that he dies and has dropped the samples. I'm not with him at the time, but I figure he'll pick them up when he can. Things get hairy for a bit and everyone dies a few times, but we finally finish the last objective.
Then I notice we don't have the samples. I check the map and see there are some sample icons, so I figure that one of those must be the super samples. But after running to pick them up, we still don't have the super samples. So I say in voice chat, "Did anyone see where that dude dropped the super samples?" And it turns out he DID have voice chat turned on, because he responds, "Sorry I lost them."
I will admit that I lost my cool. I didn't say anything, but I kicked him from the game. I probably shouldn't have, since I should have used it as a learning opportunity. I was just frustrated because I specifically said what I was doing, then when he made a mistake and took the samples, I told him immediately and he didn't listen.