Harold & Maude
I couldn't find a clip of that scene, but in my search I did come across this webpage, that just made me so happy for its delightful-ness, I had to share.
If you want to sing out, sing out. And if you want to be free, be free. 'Cause there's a million things to be you know that there are!
My mother introduced me to this movie in 9th grade. This says a lot about me, my mother, and our family. ;-)