Bum Rap Meaning

(idiomatic) An undeservedly unfavorable portrayal or reputation.

Example: 1918, "Hun Talk," Chicago Daily Tribune, 7 Oct., p. 17:
  . . . going over the top of the wall of the Trenton prison, where I was sent on a bum rap.
2008 Sep. 10, Patti Neighmond, "Study: Arthroscopic Surgery Provides Few Benefits," National Public Radio (retrieved 24 Mar 2009):
  Orthopedic surgeon Robert Marx, with New York's Hospital for Special Surgery, says that findings from the current study should not give arthroscopic knee surgery a bum rap.