Ganguro is a fashion trend in Japan where teenage girls try to emulate the tan bimbos of America. It started with a little bronzer but escalated into full black face and pink 80s hair. Extreme Ganguro girls are called Yamanba, which roughly translates to mountain hag. This isn't a derogatory term, these girls are actually trying to go for the mountain hag look.
...and I thought hipsters were bad.