Usually used by indie kids to make fun of scenesters. It takes the phrase hard core and it's usage in the word "hardxcore," and transforms it into "scenexcore," roughly meaning very scene.
OMGZZ!!! That shirt is so scenexcore! You're scenexcore like woah!
WOAH. UR NEW UNLABELED BAND PINS ARE SOOOOO SCENEXCORE!!
An expression of frustration meaning "hitting your head on a desk." (The *s signify an action.)
I'm so freaked out about this test! *headdesk*
I can't believe that he hasn't called back!! *headdesk*