Couple of things:
1) When using bluff in combat, instead of "Hey sailor!" yell out "Your shoe's untied!" That's more the effect you get.
2) Fortification bypass such as precision will not always allow sneak attacks. Some mobs have "Immunity to sneak attack" as well as some amount of fortification. Those mobs - most undead, plants, etc - can not be hit with sneak attack damage even if you have lots and lots of fortification bypass. However, the top auto-grant ability from Shadowdancer Epic Destiny and the new core ability from the Assassin enhancements, Assassin's Trick, will also remove some or all of a mob's immunity to sneak attack - this will let you sneak attack anything!
FYI - the Truthful One in FoT appears to have no immunity to sneak attack at all, as far as I can tell.