Mariah Carey's Ex-Fiance James Packer Feeling Blue in Tahiti

Mariah Carey's ex-fiance is letting loose these days ... at least that's how he rolls on vacay.

James Packer was aboard his yacht in Tahiti Thursday ... and from the look of things, he's still reeling from his split with Mimi last October.

It was pretty nasty -- she burned her $250k wedding dress and demanded $50 mil claiming he uprooted her from her life in NYC and caused emotional distress after canceling the South American leg of her world tour.