I have been pondering this for a while, unable to pin down a particular song. A light bulb came on yesterday when Johnny Walker played Bohemian Rhapsody on Sounds of the Seventies. Other than nursery songs (Puff the Magic Dragon, Morningtown Ride, Two Little Boys etc.) I didn't like pop music at all in my early childhood. I found glam rock a bit scary and other early seventies stuff (which I now love) seemed too grown up and sophisticated. Bohemian Rhapsody was probably the first time I liked a record that my parents did too. It marked the start of my interest in music.
The other track that springs to mind is Geno by Dexys Midnight Runners. They were the first band I ever saw live. A friend and I sneaked out to a local nightclub where they were playing (early eighties). Despite being under-aged, my friend (who knew the club owner) got us in through the back door in exchange for us helping to load the band's kit onto their van after the concert. As "staff" we managed to get right in front of the stage, right in front of the brass section belting out the chorus to Geno. The raw power of those sax's, trumpets and trombones totally blew my mind. I still get goosebumps thinking about it.