A hipster ghetto is the neighborhood of a major city that all the hipsters seem to congregate in. Examples:
New York City - Williamsburg
Chicago - Wicker Park
Los Angeles - Silver Lake
Boston - Allston
Seattle - Capitol Hill
San Francisco - Mission District
Portland - anywhere...
Frat Bro Mike: Oy, let's go get wasted in Allston tonight.
Frat Bro Jake: Screw that man, it's a hipster ghetto.