RORY: Hey, how’s Diane?
CHRISTOPHER: Uh, Diane is ancient history.
RORY: When I met her at Easter you said she could be the one.
CHRISTOPHER: The one to be gone by Memorial Day.
Memorial Day is a public holiday in the United States to remember those who have died while serving in the armed forces. It’s observed on the last Monday of May, which in 2000 was May 29. It is commemorated with military parades, and by decorating the graves of fallen soldiers with American flags. Memorial Day is considered the unofficial start of summer.
Christopher brought his girlfriend Diane to meet Rory at Easter in 2000, which would have been April 23, telling her that the relationship was serious and possibly permanent. About a month later, the relationship with Diane was over, yet he doesn’t bother telling Rory that until March 2001.
There’s been almost of year of phone calls from Christopher, yet he hasn’t thought to fill Rory in on a significant event in his life such as breaking up with a supposedly serious girlfriend he was thinking of marrying.
The writer (Daniel Palladino for this episode) is keen to drum it in that Christopher is an inattentive father, but it also means that Rory and Lorelai haven’t bothered asking him how Diane is in all that time either – even after she didn’t turn up to Christmas with him (unless Christopher kept fobbing them off with evasive answers).