Crimson mist, when does it work?

Could it be allowed under extremely stressful circumstances? Like when a barbarian is being overpowered by a greater number of opponents? Or being nearly killed by a formidable adversary?

Barbarians do not fear death, but it seems to me that under very stressful situations when their lives are threatened, a save versus fear to enter a rage is in place. This could represent their strong will to live.
I don't have the book in front of me, but from what I can recall, crimson mist only comes in play during a fear save situation. So, if you wish to have a horde of mauraders attacking your barbarian, and you feel a fear save should ensue, then do it.

If you are the DM it is your call. The rules are not written in stone as some people think they are. Change it if you wish.
I thought that Fighting madness added to the number of times you can use Crimson mist or the length of usage. Well, perhaps I just need to reread the feat.
Nope. Lets you enter the fighting madness once per day as a free action whenever you want. Well, except that you cannot enter a fighting madness when you are under the effect of Crimson Mist.
I thought we could give barbarians another oportunity to use crimson mist, besides:

If they succeed the save, do they have an option as to wether or not they enter the crimson mist? Let's say the saving throw is provoqued by a demon or something nasty a character in their good sense would not face, specially if most of his companions are running away screaming. Could he choose not to enter the rage, and run away in his good sense? After all barbarians are survivors, not ravenous beasts that jump discriminately on whatever threatens them enough to force a save vs fear.

Fighting madness is restricted to certain races, so crimson mist is the prevalent ability of barbarians.
Ah, yes, you are quite correct Vince. Goes to show just how much I remember the rules.

Voltumna, yes if the save was made, he/she could run away.Unless the enemy was picts. Especially if they were picts. Why run away from mere Picts? They should be wiped out.