to suddenly change from happy-go-lucky and cheerful to moody and angst ridden. Often as a result of a breakup (such as Alanis Morisettes's with Dave Coulier)
Megan: NO, I don't want to go to the mall! I can't believe that stupid ass cheated on me. I don't think I'm ever going to be the same. I'm going to sit in my room and listen to angst-ridden music.