An interesting phenomenon is a group adopting a slur as its nickname. For example, the Prime Minister of Great Britain is, officially, a Conservative, but all sides use “Tory” as a synonym for his party, even though “Tory” originated as a slur:

The word “Tory” derives from the Middle Irish word tóraidhe; modern Irish tóraí: outlaw, robber or brigand, from the Irish word tóir, meaning “pursuit”, since outlaws were “pursued men”.[4][5] It was originally used to refer to an Irish outlaw and later applied to Confederates or Royalists in arms.[6] The term was thus originally a term of abuse, “an Irish rebel”, before being adopted as a political label in the same way as Whig.

Similarly, the Liberal Party that thrived up through World War I was nicknamed the Whigs:

The term Whig was originally short for “whiggamor”, a term meaning “cattle driver” used to describe western Scots who came to Leith for corn. In the reign of Charles I the term was used during Wars of the Three Kingdoms to refer derisively to a radical faction of the Scottish Covenanters who called themselves the “Kirk Party” (see the Whiggamore Raid). It was then applied to Scottish Presbyterian rebels who were against the King’s Episcopalian order in Scotland.[1] The term “Whig” entered English political discourse during the Exclusion Bill crisis of 1678–1681 when there was controversy about whether or not King Charles II’s brother, James, should be allowed to succeed to the throne on Charles’s death. “Whig” was a term of abuse applied to those who wanted to exclude James on the grounds that he was a Roman Catholic.

“Quakers” and “impressionists” also took their names from attacks on themselves. Two of the most successful major league baseball franchises, the New York Yankees and the Brooklyn/Los Angeles Dodgers, take their names from pejoratives:

Trolley dodger was a pejorative term of Manhattanites for residents of Brooklyn, New York from the late 19th century to the middle of the 20th century. The term, relating to Brooklyn’s preponderance of trolley lines, was the basis for the name of the Major League Baseball team the Brooklyn Dodgers (which moved to Los Angeles in 1958). Although they had a variety of nicknames before the 1930s, the “Dodgers” name first arose in 1891, when their field in Eastern Park was bordered on two sides by trolley tracks.

In college sports, ethnic and regional slurs are occasionally seen: the Notre Dame Fighting Irish, the Oklahoma Sooners. Some other popular team names that sound like slurs are at best ambiguous in origin: the Indiana Hoosiers, the Nebraska Cornhuskers, the Purdue Boilermakers, and the Texas A&M Aggies.