This is my first attempt at a guide to what is seemingly a difficult achievement. I had trouble getting this to unlock myself so i will just explain what i did and hopefully it may help you.
Firstly i unlocked all the clothing over the course of career mode for female, in both star and superstar mode.
Whilst i was completing the female career i wore all of the clothes and hair pieces(including colour variations) for one song each making a note of which items i had worn. When i completed the female career on star and superstar i began to sing the songs solo to finish off wearing the items i had unlocked for completing the career. When i finished wearing everything no achievement appeared so i began work on the male career.
I did the same for this career, did star and superstar careers whilst wearing the items. I am pretty sure there were less items for the men. Again when i unlocked the last items for completing the careers i began to work on the solo songs again were i finished off wearing all the clothes. Again i wore everything but no achiement.
By this time i was very bored and annoyed coz not only had the fashion victim achievement not popped but neither had the one for singing the solo songs.
It finally popped in the clothing menu after selecting an item i had already worn but not in every colour variation.
This seemed a little glitchy to me but my husband has a theory about it. He does not think that the game saves which items you have worn, so if you quit the game you lose all of your progress towards the achievement.
This would explain why I wore the entire set of clothing three times without success (quitting out to play other things etc), but on the occasion where I ran through it without stopping the achievement popped (same goes for solo songs too).
I would advise that once you start working towards Fashion Victim you do not quit until it gives you the achievement. Hopefully this will make it pop when each item has been worn only once.
You could also try just selecting each item of clothing one after the other without singing, as the fact that the achievement unlocked in the menu would seem to suggest that could work.