Necro Feign Death Spell

[Ahhah Hah]

Sometimes it works and sometimes it does not.
Observe your opponent and if he does not stop rushing at you kite him further and re-FD and observe him again.
On some monsters I've found that you need to FD 3-4 times before it truely clears aggro, even if they leave you alone after you've fallen to the floor.
If 3-4 FD's does not clear aggro (when you sit up they rush back at you), I would FD and /q.