In S1E18, Gran is scolding Lorelai and Emily for arguing. Gran says, “Raising your voice during high tea, who ever heard of such a thing? It’s like Fergie all over again.”
CORRECTION: As several lovely commenters have noted, Gran is certainly referring to Fergie, Duchess of York. I don’t know why I had Fergie, the musician from the Black-Eyed Peas, in my head (I think it’s because Gran talks about Korn and how nice they are, so I had musicians on my mind).
Anyway, Fergie is also known as Sarah, Duchess of York. She was married to Prince Andrew in 1986, but they separated in 1992. Later that year, tabloids released photos of Fergie sunbathing topless with another man, and the Duke and Duchess officially divorced in 1996.
Thanks for keeping me on the right track, readers!