Type your answer here... i think,an Iranian handicraft is relatively cheap and high class for giveing to a friend
Give them a gift.
This website, http://friendship.about.com/od/Gift-Giving/a/Gift-Ideas-For-Your-Best-Friend.htm, lists great ideas for your best friend who is turning 18. From that list, I think a friendship bracelet or a handwritten gift would be the best gift.
Something that they like. Since they're your best friend you should know what they want.
If one wishes to give a best friend a necklace as a gift this can be done for any occasion. One can choose to provide a gift like this for a birthday, Christmas or just as a spur of the moment surprise gift to express your friendship with the best friend.
A love letter.
Friendship
I would have to say something that represents your guys friedship
What about a piece of jewelry.
take her 4 a wallk by the beach
Your treasure box.
For a male best friend you could buy him something as simple as a tie or shoes or belt. If you really had no idea, get him a gift card. But the best option would be something funny to make him laugh.
To put it on your arms and take it over to your friend