Aladdin and Jasmine in Aladdin
For the live-action adaption of this Disney classic, the costume designers decided to dress up the main characters a bit more. That meant that Aladdin wore a shirt, and Jasmine covered up her midriff. Most people were shocked that the filmmakers lost the pair's iconic costumes, but the designers claimed it would be better for them to cover up in 2019.
Green Lantern in Green Lantern
I know, we don't like to talk about Green Lantern... But, we have to. The design team decided to go full CGI for the costume. Sadly, it was extremely obvious that Green Lantern's costume was all computer images. The directors said that they wanted to try something innovative but realized it backfired.