I did have this one time where someone ninja-killed a rare that I was standing next to while waiting for a friend to come. This was before Lich King's time but not long before. At the old guild I used to run at the time, I had a guildie whom I had a place in my heart for for many reasons. This also includes helping her tame rares or just plain pretty pets on her hunter. So, when she mentioned she had a thing for tallstriders, I mentioned Mazzranache first. Then one random night when I decided to check and see if that flamingo was around in Mulgore after landing in TB, there she was (however gender you look at for Mazz). Mazz striding (nice pun there) conveniently among the rolling plains. I instantly told my guildie and she was well on her way. Unfortunately, she was a lowbie so she did not have a flight path to TB, a mount, or the cheetah aspect. It took her awhile to try to come while I was walking next to Mazz but not too close. Then, all of a sudden, a lowbie tauren hunter came by and slaughtered the poor bird in front of me. After the bird was dead, I asked him why he did it. I was saving her for a guildie. No answer. I either suspected that player was on a trial account or plain griefing. My guildie was disappointed, whether she was there or not.
It really is cruel for players to ninja-kill rare pets hunters are trying to tame to massage their ego or someone else's. I, myself, used to make a small business by informing any hunters in the area if they want this certain rare pet that I am staring at. Either I would be calmly watching them make the tame, use a Freezing Trap if they didn't have the spell, and/or attack any adds or stray mobs the rare might attract (like Dishu for example) so the hunters themselves don't die.
Have another small story. When I was at the Barrens just checking out to see if Humar was around (not that I wanted him; I had Araga instead

). He wasn't but there was a hunter who built a temporary treehouse near his spawn point waiting for him to appear. At first, the hunter thought I wanted Humar, too, but I said I wasn't interested and I (and a guildie later) ended up keeping him company while we waited. We must have waited about a couple hours. Then a level 62 orc hunter showed but only for a few minutes (we were all horde, btw). Then all of a sudden, our buddy hunter DC's...and at the worst time, too. Humar showed up shortly after. Me and my guildie prayed for him to come back on as the lion was sleeping peacefully next to the tree. He never came back and the same orc hunter we saw earlier ended up taming Humar. The next two nights, the buddy hunter logged on and I whispered him Humar showed right after he DCed and another hunter got him. The rest of my experience with this hunter is fuzzy after that, but I think I was able to help him tame Azzere. I don't quite remember if it was him I helped but I remembered letting someone know Azzere was around if they wanted him.
Another EDIT: I guess my small string of stories does always end with a happy note. Re-editted as posting the other half in the rehome thread will do, too. Thankees though.
