Back Track 5. Now Kali Linux.
I had not suitably prepared. I was a Windows Vista power user who heard how I could crack some Wi-Fi and gave it a whirl.
My chips went into one basket and me, oh my, was the transition ever so uncomfortable. What was dual booting? Who knows. Long story short, I made a mess for myself. I went through a significantly steeper learning curve than most, though it introduced me to script kiddie tools, programming, and eventually exploits.
Now a decade or so later, I've settled away from Arch to Debian. Though I miss the bleeding edge, my update frequency has lost much of it's zealous edge.