"My bad" is an American idiom

Idiom

Idiom is an expression, word, or phrase that has a figurative meaning that is comprehended in regard to a common use of that expression that is separate from the literal meaning or definition of the words of which it is made...

 that was made popular by Manute Bol

Manute Bol

Manute Bol was a Sudanese-born basketball player and activist. At 7 feet, 7 inches , Bol was one of the tallest players ever to appear in the National Basketball Association, along with Gheorghe Mureşan. Unlike Mureşan, however, Bol was naturally tall and did not have a Pituitary disease...

 although it was also used before his arrival in the USA. It usually means "my fault", "my mistake", "I apologize" or "mea culpa

Mea Culpa

Mea culpa is a Latin phrase that translates into English as "my mistake" or "my fault". To emphasize the message, the adjective "maxima" may be inserted, resulting in "mea maxima culpa," which would translate as "my most [grievous] fault."...

". It gained popularity with urban players of streetball

Streetball

Streetball or street basketball is a variation of the sport of basketball, typically played on outdoor courts and featuring significantly less by way of formal structure and enforcement of the game's rules...

 and then spread into mainstream popularity. Its use in the 1995 film Clueless greatly increased the phrase's popularity.