If the highlight of The Apprentice's admittedly superior first season was Donald's rattlesnake hiss ''You're fired!,'' his now-patented catchphrase has been trumped in season 2 by sidekick Carolyn's smoother, deadlier ''You failed.'' While her boss has quickly bloated into a product-shilling caricature, 35-year-old Carolyn Kepcher is sharper, scarier, and now the main reason to tune in to NBC on Thursday nights. Impress her and she'll give you a motherly nod. Disappoint her by, say, calling her Caroline, as one dim-bulbed member of the boys' team did and she'll shred you with one of her icy-blue looks of disgust. (If only that could be trademarked.) Donald, no fool, knows the score. Notice how whenever he makes one of his boardroom slashes, he looks first to his left for Carolyn's Cheney-like nod of approval. (Poor George, Trump's underutilized henchman to his right, looks like he'd be put to better use checking the contestants' coats.) But the mother of two would like you to know that she keeps her bitchiness to the boardroom. ''People come up to me all the time and say, 'Well, you're actually a very nice person!''' says Carolyn. ''And I'm like, Imagine that! I am.''