TheCrimson Nosferatu will start to spawn into the map after the player opens the coffin in the Cemetery in order to obtain the Nosferatu Chaos Material for Alistair's Annihilator.
There are two ways you can go about getting this achievement.
1. Let the one you spawn from the coffin to bite you.
2. Let one natural spawn after the coffin to bite you.
After the Crimson Nosferatu jumps off you even if you go down afterwards you will get the achievement.