Great topic. There are so many. That was a wild decade.
But here's a few that take me back.
This solves a 'what film was this' mystery that has played on my mind for years and years. When I was a kid, I saw a movie on television with a scene that involved a woman washing a car, and what seemed like prison inmates working on the road and going bananas while watching her.
The movie itself is not Car Wash: it is Cool Hand Luke (1967). Not a 70's movie, but kind of close.
Much thanks to Hammock Rider for prompting this merry trail of association!