Roppongi
Enough said.
This place is insane. It's 6 am and I am about to go to bed, 3rd night in a row. These people party from the PM to 9 am every day. I want to live here. I haven't had this much to drink in my entire life. I haven't danced for 14 hours before. I haven't ever gotten cheap sushi right next to Tokyo tower before forgetting who I am for 3 days. Mission accomplished. Make a visit here, it would be worth every penny.