For fans, the whole list is worth a read, but some of the better terms are:
You look beautiful tonight: This is a Paula Abdul expression meaning “You can’t sing.” It is slightly different from “You’re a beautiful girl,” which means “You can’t sing, and you’re probably going to be eliminated this week.”
You’re current (or “relevant”): “Every time I look at you, I can feel myself and my business partners growing richer and more powerful.” Generally, this is said when a contestant bears some particular resemblance to some strand of popular culture, such as the current attention given the fact that Adam Lambert has dark hair and looks at people as if he wants to devour them in an unsavory fashion, and that reminds the judges of vampires, and that reminds the judges of “Twilight,” which is popular, which means Adam Lambert is “current.” This is not, in other words, a construct with a lot of integrity.
Yo yo yo yo/what’s up?: Often, Randy Jackson begins critiques with either some number of “yo”s, or with questions about the contestant’s well-being. If he offers one “yo,” that is usually bad news. More than one “yo,” particularly if he makes it to four “yo”s, is good or very good news. Questions about how you’re doing — “How are you?” “How you feeling?” “How you doing?” etc. — generally mean he hated your performance but pities you. Occasionally, he starts a critique by laughing, which means, “I don’t know who’s voting for you, but apparently someone is.”
You know who you are: Taken literally, this might be considered damning with faint praise. In context, however, it means, “You sing the same way every week, and we have decided that’s a good thing.”
I want to see you stretch: “You sing the same way every week, and we have decided that’s a bad thing.”