It is a sarcastic way of saying "I don't care" to someone who is complaining about something. Or, more literally, it means, keep on crying to me... until you have cried enough to fill a river.

"Cry me a river" is a term used mostly in a sarcastic way to tell someone that even if they apologized, cried, complained or whined in front of you, you wouldn't bother to or care for that -in an unsympathetic way. A famous example is the hit song, "Cry me a River" by Justin Timberlake. The song is about a brokenhearted man (Justin) who learns about his cheating girlfriend but he doesn't bother to forgive her once he finds out - means he's telling her to "cry him a river" (cry buckets and buckets of tears which is not possible) but he won't bother, care or forgive her. You can read the lyrics of the song to understand better http://www.metrolyrics.com/cry-me-a-river-lyrics-justin-timberlake.html and the video of the song https://www.youtube.com/watch?v=DksSPZTZES0&ob=av2n

"Cry Me a River" is a popular American torch song, written by Arthur Hamilton and first published in 1953, and made famous in the version by Julie London, 1955. A jazzy blues ballad, "Cry Me a River" was originally written for Ella Fitzgerald to sing in the 1920s-set film, Pete Kelly's Blues (released 1955), but the song was dropped. Fitzgerald first released a recording of the song on Clap Hands, Here Comes Charlie! in 1961. The song's first release was by actress/singer Julie London in 1955, backed by Barney Kessel on guitar and Ray Leatherwood on bass. A performance of the song by London in the 1956 film The Girl Can't Help It helped to make it a bestseller (reaching nr. 9 on US and nr. 22 on UK charts). London's recording was later featured in the soundtracks for the movies Passion of Mind (2000), and V for Vendetta (2005).----Wikipedia @ http://en.wikipedia.org/wiki/Cry_Me_a_River One of the best performances, or at least a representative performance or the Torch Song "Cry Me A River" is performed by Joan Baez as follows: . https://www.youtube.com/watch?v=AjgzSGsjTp0