Around here, it seems that the new word going around the teenage community is "childish"
meaning, in order of commonality:
or as an adjective used to describe someone in authority (ex. You won't let me loiter in the hallways between classes with my twenty other friends? Stop being so childish!)
Other examples include:
Talking in a movie theater? Stop being so childish!
That garbage outside sure smells childish.
First graders have a childish intelligence level.
Edit: Also, around the gaming community there's "natural", stemming from a "natural twenty" meaning a critical hit.
It's used in the same way "boss" is. Essentially, radical, awesome, unpredictable, victorious, etc.
ex. That backflip you just flawlessly performed was so natural!
A lightning bolt struck right outside my house? How natural was that???