To get it...FIRST go and log in to stardoll as usual...then click here:
http://www.stardoll.com/en/campaign/?id=5
The third task will be on.. The correct answer is "Report and block the user"
Submit it and the dress will arrinve in your suite after a while.
I'm guessing that if you already own it or used to own it...you won't be getting it again..
...xoxo M_Themis