“Park Sloper” is the name of an inhabitant of Park Slope, in the borough of Brooklyn. The name “Park Sloper” has been cited in print since at least 1907.
   
 
Wikipedia: Park Slope, Brooklyn
Park Slope is a neighborhood in western Brooklyn, New York City’s most populous borough. Park Slope is roughly bounded by Prospect Park West to the east, Fourth Avenue to the west, Flatbush Avenue to the north, and Prospect Expressway to the south, though other definitions are sometimes offered. Generally the section from Flatbush Ave. to Garfield Place (the “named streets”) are considered the North Slope, 1st St. through 9th Street is considered the “Center Slope” and 10th St. through the Prospect Expressway is the “South Slope.” The neighborhood takes its name from its location on the western slope of neighboring Prospect Park. Fifth Avenue and Seventh Avenue are its primary commercial streets, while its east-west side streets are populated by many brownstones.
 
23 February 1907, Philadelphia (PA) Inquirer, “Burglar Led Lively Chase In Brooklyn,” pg. 1 col. 1:
NEW YORK, June 22.—The noisiest, most picturesque an still most unsuccessful burglar hunt that ever occurred on the Park Slope in Brooklyn, began at two o’clock this morning. (...) The Park Slopers, moreover, have been sleeping on their guns for the past month or so, ...
 
Google Books
By Quentin Reynolds
By Quentin James Reynolds
New York, NY: McGraw-Hill
1963
Pg. 14:
The Flatbusher has difficulty following the speech of the Greenpointer, the native of Brownsville has about as much in common with the Park Sloper as he would have with someone from Fort Worth, Texas.
     
Google Books
Buying and Renovating a House in the City:
A Practical Guide
By Deirdre Stanforth and Martha Stamm Connell
New York, NY: Knopf
1972  
Pg. 67:
Park Slopers take more interest in Prospect Park, Brooklyn Museum, the Botanic Gardens, and the Brooklyn Public Library and Academy of Music.
 
New York (NY) Times
May 18, 2008
FIRST PERSON
Park Slope: Where Is the Love?
By LYNN HARRIS
(...)
Park Slope also may provide a peek into a crystal ball that some don’t want to see. “Hipsters and people who don’t have kids are terrified of becoming grown-ups and parents, which is what Park Slope has come to represent,” said Jeff Sandgrund, 30, a lifelong Park Sloper.
 
Park Slope Patch
AROUND THE SLOPE
By Louise Crawford
June 27, 2011
Opinion, The Neighborhood Files
Will The Real Park Sloper Please Stand Up
Part one of a two part series.
So, who’s a real Park Sloper? Are there people who have a more legitimate claim to this neighborhood than others? Do you have to have been born here—or to have moved here before a certain date—to be considered authentic?
   
Eater—New York
Park Slopers now Have the Kosher French Bistro They Didn’t Know They Needed
Wednesday, March 6, 2013, by Alexander Hancock
Belleville was not the most noteworthy restaurant in Park Slope. It was an sometimes-okay, occasionally-troubled French bistro that flirted with shutter for years.