Most commonly the word is used as a derogotory term for anyone who, knowingly or accidentally, uses and word or phrase which is part of the yinz dialogue of english as commonly spoken in Pittsburgh.

Yinzer can also, with a much more neutral tendancy, refer to anyone from the greater Pittsburgh area. The term has become popular among Pittsburgh expatriots who will occasionally recognize a hint of the yinz accent in an individual while far from Pittsburgh.

Odd how homesickness can turn a con into a pro, isn't it?