Trick is, I know almost nothing about the movie, I just remember two scenes. First is of no use, as it is just a car plus two people. I think it is somewhere in rural US, in the sixties, but I can be wrong. Hopefully second scene should do the trick. Group of people aged about twenty. There is a party. A girl came to this party and she is there for the first time. To become "member" (or something) she has to strip down on the pool springboard. She does it predenting she lost equilbrium and sits down.
I have seen fragments many years ago and I wanted to see the movie one day - but I forgot the title. Could it be "The Last Picture Show"?