A "thirty something" that wears clothing resembling that of a teenager. A mother who dresses like her daughter. A man in his midlife dressed as a skater.
There are many Gruppy examples out on the street, just look around you. Usually they are people who are in denial that they are getting older. Clutching desparately to their youth, using appearance as a tool to try and fool those around. This term was recently coined by a New York Fashion Magazine.
A green-oriented yuppy (i.e., gruppy = green + yuppy). Typically, one who works and/or lives in the city and lives an eco-friendly lifestyle. Often, given to trashing mainstream "pop culture" for conspicuous consumption while lavishly consuming many eco-friendly products to demonstrate a profound lack of consumerism.
While she wasn't exactly a hipster, the rain-driven drip-system she employed to grow herbs outside her 3rd story apartment showed she was very much a gruppy.