Fairy Godmother song at party?

Rating: 8/10 (11 June 2004)

Hey everyone, I was wondering about the song that the Fairy Godmother sang during the wedding party, when she's on top of the piano. I was just wondering if it's a remake of an older version of song? Or is she just impersonating someone? Some older people that were sitting in front of me were singing along with it and were busting up while she was singing.
Were they just amused elderly people or is there an inside joke that I'm missing?
"...you're tellin' me that there's no hope, I'm tellin' you you're wrong..."