As the last bars of Britney Spears’ “3” faded and another pop song began during spin class last Sunday morning, my fellow spinner, Linda, said, “Ugh, that song is disgusting.” What did she mean? Wasn’t Britney, like, practicing dancing or something in the song? I had never paid close attention to the lyrics, other than the “1-2-3” refrain that loops throughout. “It’s about having a threesome,” Linda shouted over the music. “You know, a ménage a trois.” And sure enough, when I got home to Google the lyrics, the former Mouseketeer is apparently looking for some harmless fun and implores two …