One of the things I hated during a festivity in the Rift:
Fight 4 brawlers while being surrounded by neutral people (white outline).
Accidently attacked someone else and it's a bounty for me!
(good thing I needed to log out anyway. Time solved bounty for free )
So yeah, an option to disable "friendly fire" would be nice. You'd have to turn it on again when you want some bait or rob / kill a guy, but it has my vote.
Used to be awesome in PvP when there were deer in cyrodiil.
Used to be able to take cover in a herd of deer, and also use them for healing with the 9% regen all stats on death on the soul magic dot