Deus Ex 2: The Invisible War Easter Egg - Secret Dance Party

1) In order to activate this easter egg, you need to be in the UNATCO Ruins (last level).
2) Pick up the UNATCO flag at the entrance (it's where the eye-scanner used to be in Deus Ex).
3) Walk to Manderley's old office, drop the flag and flush the toilet.

Note:
Apparently, this is a combination between the Dance Party and the Quote easter eggs from Deus Ex.