You say “sexy girl” in Hawaiian like this:
"wahine hoʻokola "
Remember, however that the word “sexy” is used just about everywhere in the world right now, including Hawaii, so you could just say “wahine sexy”.
If you wanted to say beautiful girl, you would say “wahine nani”. This might be a better choice of words when you meet someone for the first time, but this depends on the context.
If you want to learn more words in Hawaiian, you can turn to the Hawaiian electronic library. This resource contains hundreds of words in Hawaiian, so there is something new to learn every day.
Since 1978, Hawaii has had two official languages; English and Hawaiian. If you are looking to communicate with someone on the island, the chances are good that they will speak English.
Do you want to learn how to say “good luck” in Hawaiian? Click here.