From the SRD:
I'm not seeing where any special concentration or patience is required to make a sneak attack.
It takes no more time to make a sneak attack than a normal attack (because you can sneak attack on an AoO and you can sneak attack with every single attack you have), so you don't need to be patient to line up the shot.
It seems to be that the sneak attack described in the PHB is more of a reflexive strike at a vital area when you see an opening than a carefully planned attack.
*shrug* I can find no support in the rules for denying the sneak attack ability to a raging barbarian.
If you don't want to allow it, it would be a house rule on your part.
Sneak Attack: Any time the rogue's target would be denied a Dexterity bonus to AC (whether the target actually has a Dexterity bonus or not), or when the rogue flanks the target, the rogue's attack deals extra damage. The extra damage is +1d6 at 1st level and an additional 1d6 every two levels thereafter. Should the rogue score a critical hit with a sneak attack, this extra damage is not multiplied.
Ranged attacks can only count as sneak attacks if the target is within 30 feet. The rogue can't strike with deadly accuracy from beyond that range.
With a sap (blackjack) or an unarmed strike, the rogue can make a sneak attack that deals subdual damage instead of normal damage. The rogue cannot use a weapon that deals normal damage to deal subdual damage in a sneak attack, not even with the usual –4 penalty.
A rogue can only sneak attack a living creature with a discernible anatomy. Any creature that is immune to critical hits is also not vulnerable to sneak attacks. The rogue must be able to see the target well enough to pick out a vital spot and must be able to reach a vital spot. The rogue cannot sneak attack while striking a creature with concealment or striking the limbs of a creature whose vitals are beyond reach.
I'm not seeing where any special concentration or patience is required to make a sneak attack.
It takes no more time to make a sneak attack than a normal attack (because you can sneak attack on an AoO and you can sneak attack with every single attack you have), so you don't need to be patient to line up the shot.
It seems to be that the sneak attack described in the PHB is more of a reflexive strike at a vital area when you see an opening than a carefully planned attack.
*shrug* I can find no support in the rules for denying the sneak attack ability to a raging barbarian.
If you don't want to allow it, it would be a house rule on your part.