Fashion Victim achievement in Sleeping Dogs: Definitive Edition

I would just like to add my experience getting this achievement on the Xbox One version of the game.

I found that you indeed do need to buy all the DLC outfits to get this achievement. I had collected 100% of the lockboxes, then went to all 13 clothing stores and bought all clothes, but no achievement popped. I even went back to every store again to double check to make sure I didn't miss anything but I hadn't. I then did a few car theft missions for Tran to save up money, and once I had enough cash I went to the "legendary" clothing store where DLC outfits are located in the Night Market. Once I bought the last outfit from that vendor, the achievement immediately popped.

I did find this odd considering I did already pop the achievement for buying all the cars, and I never bought any of the DLC vehicles. That achievement unlocked right after I purchased the last vehicle from the regular car shops.

I hope this helps if you are having trouble getting this to unlock like I did.