Great movie, really great! I loved it so much. I rate it on for 12+, not because it's inappropriate for younger viewers, it's just that children under 12 might not understand most of the jokes/sensual scenes.
Violence - Isn't really an issue, the worst is maybe an attempt at a fist fight.
Sex - A character is briefly shown in her bra, characters are seen making out several times, at the drive-in a character makes a pass at another character, sexual words are spoken when two characters talk about a broken condom resulting in a character's fear that she may be pregnant, bare butts are seen when some characters moon a television camera, male characters discuss female anatomy, one male looks up the skirts of a female student, female characters dance around in their lingerie making fun of a character's virginity, the song "Greased Lightnin" has some mild sexual content..
Language - Mild. Just like "sh-t", "t-ts", "dammit", etc. Mostly sexual content.
Drinking, smoking, drugs - Lots of the "cool" characters smoke and drink. At a slumber party, female characters persuade another female character to try some wine and to try smoking. She does.