Ever wonder where the idea for some hit tunes come from? Like The Knack’s 1979 hit “My Sharona?” Well, if you believe this video, it was named after a 17-year-old girl who lead singer Doug Fieger, then 25, had just met … even though he already had a girlfriend, but was still so obsessed he wrote a song about her! I’ll let the video tell the rest of the story–and…