JERMAINE Dupri had a little too much of a good time celebrating his 36th birthday. The other night, Dupri and his squeeze, Janet Jackson, went to Tenjune, where, spies say, they shared bottles of Jay-Z's Ace of Spades Champagne and Patrón tequila with Ne-Yo, Busta Rhymes and Ice-T - until Dupri "vomited in Janet's lap. Ms. Jackson bolted out of the scene and sped off in her chauffeured Maybach." A rep for Jackson and Dupri didn't return calls. A rep for Tenjune declined to comment. Meanwhile, we hear Dupri is under some stress at work. The head of urban music for Island/Def Jam put out his lady's last album, "Discipline," which flopped. Our insider said, "[IDJ head] L.A. Reid had wanted to make changes to the album, make it fresher with some newer artists added in, but Janet said no - and Jermaine backed her up. He looks silly right now."