1) Informal apology 2) Mea culpa, late-1990s style 3) Modern apology 4) Oopsy 
`My bad` is an American idiom that was made popular by basketball players in playground games in the 1970s and 1980s. It usually means `my fault`, `my mistake`, `I apologize` or `mea culpa`. It gained popularity with urban players of streetball and then spread into mainstream popularity. ...