David Wells has got balls: Publishing a tell-all while wearing the Yankees' pinstripes takes major-league cojones. (Want to raise George ''Boss'' Steinbrenner's blood pressure? Tell him you pitched your 1998 perfect game half-drunk.) But that's Boomer. In his winning memoir, the 39-year-old lefty delivers on Bull Durham-like groupies, SNL parties, and teammate talk about Derek Jeter's singing (''He's Al B. Sure on crack''). He bares his heart, his soul, and (in a photo on page 360) his behind. Though Wells has caused a stir by estimating that 10-25 percent of big-leaguers are ''juiced'' on steroids (he put the figure at 25-40 percent in an earlier draft), it's his tales of champagne showers and championship seasons that will linger.