For my 16th birthday, I asked for a plain white cake. There's a big long story of how somoene stole my cake and my parents quickly got a new one, but I didn't know that until long after that birthday. But anyways, I asked for a plain white cake and asked for several bottles of sprinkles and frosting tubes. Then, I had a big group of girls come over and we all sat down and decorated the cake.
That was one of the best times I've had on my birthday, everyone decorating the cake to our hearts content.
And then for my going away party before I moved to Oregon, I had my three best friends and I decorate another big cake, and we got goofy and demolished/ate it with our bare hands.
Decorating cakes is so much fun especially when my friends and I get silly.