Quick: I'm out of touch and need a good, "fun" dinner spot in Rock Center
It's not trendy, but if your idea of a "fun" restaurant centers mostly around great food (else, why would you be here?) I recommend Wu Liang Ye.
Fabulous, authentic Szechuan cooking, and it's right by Rock Center:
Wu Liang Ye
36 W 48th St (between 5th and 6th Aves, upstairs)
New York, NY 10036
Great appetizers: dan dan noodles to make a brave man weep, though my personal favorite is the sliced beef tendon in chili vinaigrette.
For entrees, the shredded camphur tea-smoked duck with spring ginger is not to be missed.