(not sure if this is related to bpd since it's only recently I've learned about having it) Sometimes I do this because it's a more comfortable emotion for me than sadness or anxiety, kind of like a coping mechanism. It doesn't get my anger out like people say, it just makes me more angry. This kind of angry feels different though, because it isn't caused by anything undesirable. It actually kinda feels good but goes away when the music does.