Tbh Super Bass. I lived in Europe back then and it was kinda heard to hear of her mixtape stuff. I heard Super Bass and I was like "OMG she raps so fast in the verses", so I got addicted and went on Youtube, opened a lyric video and played it until I memorized EVERYTHING .
Then I googled her material and heard Itty Bitty Piggy and I went like OMG. That's when the obsession begun