19 Nov 2009 23 Nov 2009
If this achievement doesn't unlock, do not start a new character. I've done it 5 or 6 times and still it didn't unlock.
Instead, join an online game hosted by a hunter who has already unlocked this achievement. This doesn't work if you're invited by a friend, you must find someone by yourself who has created an online game. Check their gamercard using Y in the lobby, you'll see the host's class and wether he has the achievement or not.
Then kill an enemy with Sanguine. Enjoy your achievement.
While it seems very weird, this technique worked for me, and many more people.