All things considered, daily life in Japan is pretty reserved. But there's something about doing cosplay, or taking on a certain style of dress that brings down the inhibitions and lets people go wild - or just dance in public.
For years, the Rockabilly dancers have been a fixture at the front entrance of Yoyogi Park, which is just a 2-3 minute walk from Harajuku station. I don't know much about the group or how often they show up, but go there on a weekend and there's a good chance they might be there, getting down with their hair as greased back as can be. Check out the club insignia a few of them have on their jackets.