LORELAI: Michel, you know that Sookie ends up thinking she’s coming down with whatever illness other people have.
SOOKIE: Nuh uh!
LORELAI: Oh no? What was that whole conversation last week when I had to convince you, you didn’t have a prostate.
SOOKIE: Oh. How is Al?
The prostate is a gland in the male reproductive system that secretes an alkaline fluid which makes about a third of the volume of semen. The fluids helps make the vagina less acidic during intercourse, improving the lifespan of sperm.
It seems as if Al from Al’s Pancake World has a problem with his prostate. Older men often have an enlarged prostate, which isn’t actually dangerous but can cause difficulties with urination. It is usually treated with medication.
If Sookie really thought she had an enlarged prostate, perhaps she imagined that she was also having difficulties urinating, based on Al’s description of his symptoms.
The Annotated Gilmore Girls 