A friend of mine bought an electric guitar when we were about 16 or so. He was having fun with it, so I went the cheap route and borrowed a battered old acoustic guitar from my aunt, a music teacher. Many people in my family have music talent, a lot of singers and various instrument players also -- but I had never really had much interest.
Anyway, I took that acoustic over to my friend's house. Pretty sure "Smoke on the Water" was the first riff he taught me, and the first time I had that "whoa, this is so cool" moment. Some months later, I got my own electric (Epiphone Korina Explorer) as a birthday present. That is still my only electric guitar.
I never got very good, but I had fun. Never took lessons, just taught myself and compared notes with friends. "Enter Sandman" was the first song I learned relatively completely, from a tab book. But, in college I probably only played a few times per year; just as a minor hobby. BUT, I remained interested enough that I bought my first bass (Ibanez GSR200) sometime in there. Immediately clicked more with bass than I ever had with guitar.
I don't remember exactly what the first song I tried on bass was, or what song made me think that bass would be a fun thing to try. Possibly "Orion" by Metallica -- mastering that song remains a long-term stretch goal for me. But, I can definitely remember that the first song that I really got into on bass was "Like a Stone" by Audioslave. I think that was the first song for either instrument that I felt I could actually play along with solidly all the way through the song, and therefore convinced me that I was actually a bass dude instead of a guitar player.