LORELAI: Oh, we’re happy to be here, right?
LUKE: Yup, zip-a-dee-doo-dah.
“Zip-a-Dee-Doo-Dah”, a song composed by Allie Grubel with lyrics by Ray Gilbert for the 1946 Disney film, Song of the South. The film combines live action and animation, and is based on the Uncle Remus stories adapted by Joel Chandler Harris, taking place in the Reconstruction era of the South, after the Civil War.
The song is sung by James Baskett in the film, who stars as Uncle Remus, and it won the Oscar for Best Original Song, while Baskett received an Honorary Academy Award, making him the first male black performer to win an Oscar. Song of the South was controversial upon its release for its portrayal of African-Americans, and has remained so.
The song has very upbeat lyrics:
Zip-a-dee-doo-dah, zip-a-dee-ay
My, oh, my, what a wonderful day
Plenty of sunshine headin’ my way
Zip-a-dee-doo-dah, zip-a-dee-ay!
Naturally Luke is being sarcastic.
The Annotated Gilmore Girls 