I think Mike's answer is entirely   sufficient. 

Just because  people put words together,  does not mean that some "specific" meaning" can be derived  from what they write or say.  This is a  case of poor communication skills on the part of some author.

      "Leather wearing alcoholics" is not an identifiable social convention.

What the author may be referring to are  people who are both "drunk"  and "wearing leather" as

Bikers or other rough  sorts of people  do  to create a   social identity.

  Referring to "alcholics"  is an extremely vague reference,  because it refers to persons

who have no control over their  alcohol  consumption. 

As indicated by the American Medical Association,   Alcoholism is classified as a medical diagnosis.

The end  result of this is that we can see, eventually, that just because a person  is wearing "leather,"  it does not mean that the  person   is  has an Alcohol Problem.

Not everyone  drinking alcohol is an "alcholic".  

 As one popular joke informs us, the fellow says:

   "What?  Me have an alcohol problem?

I drink.   I fall down.   No problem!"

She's just sticking together a couple adjectives; "leather wearing" and "alcoholic" (turned into a noun). 

Actually, I suspect Chandler may be making a disrespectful reference to stereotypical aspects of motorcycle culture. The idea is that, supposedly bikers drink a lot and wear leather. The leather has to do not just with culture, but with practical aspects of riding motorcycles.