Bit of confusion here that I'm hoping can be cleared up. As I understand it failing a Carouse Test inflicts 1 level of Fatigue, and if you pass out as a result you become unconcious. Decadence states that you wont pass out until you have failed more tests than double your toughness bonus. To me that seems really wierd, has the Decadence Talent been written really poorly ignoring the usual rules for Fatigue, or am I missing something?

Decadence should trump Fatigue. You should consider that this is a talent that the character has and will allow him to go above and beyond what normal folk can do. Characters with this ability should be able to drink past the point where normal characters will pass out. So, yes, it ignores Fatigue rules for drinking or other drugs.

I thought it meant that it required two Carouse roll failures to accrue a level of fatigue.

Edit: I was mistaken. Literacy is a basic skill for me.

If you think of the Decadence talent as "Drink like a Kennedy (and not die!)" it is a little easier to adjudicate.

For the sake of example, let us assume we are dealing with a character with a Toughness of 33, Carrouse skill trained and the Decadence talent. JoeBob is in a brawl with a few annoyed cultists and gets a few lucky whacks in the face (ouch!). Once he racks up 3 fatigue JoeBob is "lights out" for a while from the savage beating he just took. Fortunately for our (hero?) he wakes up in a gutter several hours nursing a wicked headache and in desperate need of a new shirt. Somehow the thugs managed to miss the "emergency funds" that JoeBob keeps sewn into the lining of his overcoat and he decides that the nearby bar constitutes a suitable "emergency" under these circumstances. JoeBob buys an entire bottle of "something green" and settles down in a booth for some liquid therapy. For every drink JoeBob knocks back (defined as a shot, glass, fifth, whatever the GM rules) he tests against his Carrouse skill, with a failure earning him 1 "fatigue". Normal folks are quite done when they get to 3 fatigue, vomit in a nearby planter and pass out. JoeBob is a PRO at this stuff, having long since pickled his liver and can keep going until he hits 6 fatigue (double his TB3) or the bar throws him out.