G rating

I just saw this on one of the Kids and Family channels. I was curious as to how it got a "G" rating, as it features all of the things that usually render a film at least PG-13. It has profanity all the way through (even though the worst word here is *(note that the word I typed here was censored)*) depicts teen smoking and alcohol, and has allusions to sexual behavior. I wonder if there are any real rules about what can and can not go into a G-rated film.
(And FWIW, I am not being a total prude. I am actually wishing I could find a legitimate copy of this on DVD to buy).