Hakan's Hair
I'm willing to bet Hakan's hair is an homage to the King of Rock and Roll, Elvis Presley. It looks just like Elvis's--style, color, everything. It's fitting because Hakan is a rock musician in the movie.
On the other hand, it may just be that Burak Ozcivit's hair has that much volume and a tipping-of-the-hat to Elvis was not intended.
Whichever way it is, his hair looks so good!