For my brother's 18th birthday party, I (being 14) threw him the best birthday of his life.  He never really had much of a party because his birthday is at the very end of November. Every year he would have his party on our Thanksgiving feast, but for his 18th birthday, I called all of his friends In August and we threw his party in August.  Not only was this a surprise, but I called his work and told them to call around 9 to ask him to come to work and make him work for about 2 hours and then send him home because they didn't need him anymore. They were more than happy to do this.  So he went to work, and when he got sent home, 75 of his friends gathered in my back yard with their cars at different spots around the neighborhood and we had the whole inside of the house decorated and the back yard and pool were decorated. His girlfriend and her sister were in their bathing suits and were pretending that they wanted to go swimming or go out in the back yard and sit on the swing.  But when my brother got out there, all 75 of his friends and a few neighbors were out there and said "Happy Birthday Chris". It was a lot of fun, and my brother still hasn't forgotten about it. I was very happy to do that for him too!