Personally I kind of ignore the lyrics in this song in favour of the beat/rhythm together with Amy's voice. There are several ideas out there about the meaning of the song, one idea is that she cheated on her guy but he's ok with it since he cheated on her too so she really just 'cheated herself'.
Amy Winehouse was a British singer and songwriter most known for scandals and her raspy deep contralto vocals. She mixed several music genres, like jazz, soul and R&B. You know I'm no good comes from her second studio album Back to black (2006) and was released 2007 in the UK and 2008 in the US.
You know I'm no good by Amy Winehouse