Basically, people used to use it to mock other people for trying too hard to be "avant-garde," "experimental," or "dangerous" in some anti-societal, off-beat manner. But lately, people are using "edgy" to describe anything.
Example:
Person 1: I know everybody is bandwagoning [popular person] right now, but I really don't like their work very much.
ATRLr: your so edgy!!! drag it sis!
Example 2:
ATRLr: Do you like [basic pop star]?
ATRLr 2: No.
ATRLr: wow look so edgy! it doesn't like what i like! must be EDGY!
Example 3:
*Celebrity debuts new look*
ATRL: ****ING EDGY BITCH. DIE!!
People are essentially missing the point; because now, calling someone out for being "edgy" has basically become the new edgy thing to do. People who do it are usually trying to stand out or to look cool.
d; I can't! It isn't funny, original, or witty!
It was cute for a moment; I laughed a couple of times. But the **** got old quick.
It isn't a valid comeback, we don't think any more highly of you, and it really makes
you look like the one who's trying too hard.
Death at all the people who are going to pour in calling this thread "edgy." 
