bum rap (chiefly American)
informal noun-phrase

- blame or punishment that is unfair

Cambridge Advanced Learner's Dictionary

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WORD ORIGIN

The word bum has two distinct uses of different origins.

Among the British, bum is first and foremost used to describe the buttocks or behind. To Americans, bum is a term for a homeless person and by association refers to any worthless person or thing.

Rap has taken on many different meanings over the centuries, although the original sense referred to a quick and light blow, such as in "a rap on the knuckles," which is punishment that is not very severe and intended only as a warning.

Rap is also used in the context of a discussion (Let's rap about next week's trip to the mountains). In addition, rap is also a genre of African-American music of the 1980s and 1990s in which rhyming lyrics are chanted to a musical accompaniment.

According to the Online Etymology Dictionary, the first sense of rap as in "blame or responsibility" first appeared around 1777. Thus to get a "bum rap" is to be wrongly accused of something. This can be something as serious as being falsely accused of a crime or having an unwarranted bad reputation.

One of the most famous instances of a bum rap involved Rubin "Hurricane" Carter, an American boxer who spent nearly 20 years in prison for murder and then was released after a court determined that the original trial was unfairly conducted. In 1996 Carter, was arrested when Toronto police mistakenly identified him as a suspect believed to have sold drugs to an undercover officer. He was released after the police realised their error.

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SMUGGLE OWAD into a conversation:

"In the 1970s, Japanese cars used to get a BUM RAP, but these days they compete strongly with German manufacturers."