The characters talk about sex throughout the series.
One episode has a strip club scene, No nudity.
Some mild sexual humor.
Sex is implied in the show, but only in bedsheet cover-ups after having sex. No explicit nudity.
In Season 4 Episode 3, Rory finds a guy outside at night, who appears to be Marty, who was lying on the ground naked. Nothing explicit was seen.
In Season 5 Episode 3, Lorelai and Luke were seen in bed together after their first date. It's implied that the both of them are naked. Nothing explicit was shown.
In Season 7 Episode 3, there was a scene where Rory and Lane were at the book store. A close-up shot of a book to which Rory is reading was Henry Miller's book, Sexus. The front cover of the book is a naked body of a woman that was in black and white. Nothing too explicit.
In Season 1 Episode 17, Lorelai and Max were seen in bed together, there's no explicit nudity.
In Season 5 Episode 21, Lorelai and Luke were making out in the back of the limo. The scene cuts to the next morning in Luke's apartment. Lorelai wakes up in bed, with Luke sleeping with her.
In Season 4 Episode 22, Kirk runs out of the Dragonfly Inn with a pillow covering his private part, interrupting Lorelai and Luke's first official kiss.
Kissing, suggestive language; sex is implied, couples are shown in bed. A scene takes place in a strip club; no nudity is shown.
Some references; occasional implied sexual activity.