Skrillex Haircut EXPOSED -- Cut by Amateurs!!!

Skrillex got a haircut Friday that was worth every penny ... because it was free.

The dubstep guru hit up the Paul Mitchell beauty school in Sherman Oaks to trim his Skrillabob. The half chop would have put a $15 hole in his well-lined pocket, but it's a case of the rich getting richer.

The stylist -- who's close to graduating -- was so stoked all she wanted was a pic with Skrillex and her fellow students. Unclear why the sleepy faces.

Save the drop for the beat, Sonny.