This design was apparently a hit at a teen birthday:
Zebra Cake
You need:
Two 6-inch round cakes
Two 8-inch round cakes
Dowel rods (cut to the height of the two 8-inch cakes stacked on top of each other)
6-inch cake board, covered with foil
Buttercream frosting (3 or 4 batches)
Cake decorating bags and tips (I used tips 3 and 5)
Black and pink icing coloring paste
Ribbon
Place an 8-inch cake on a cake stand and frost with an even layer of buttercream frosting. Top with the second 8-inch cake and cover that with buttercream frosting. Smooth out the sides so that they are even.
Tint a portion of the frosting black and spoon it into a decorating bag equipped with a #5 tip. Create a zebra print pattern all over the cake, smoothing the frosting as much as possible.
Lightly press the cake board into the center of the frosting on the 8-inch cake, then remove. Use the impression as a guidline to insert the dowel rods into the cake.
Place a 6-inch cake on the cake board and frost with an even layer of buttercream frosting. Top with the second 6-inch cake and cover that with buttercream frosting. Smooth out the sides so that they are even. Center the 6-inch cakes on the dowel rods.
Use the black frosting to make a diamond shape on the front side of the cake. Change the tip on the black frosting bag to tip #3. Make polka dots all over the top layer of the cake.
Tint a small portion of the frosting pink. Pipe a the birthday number inside the black diamond on the front of the cake. Finish off with a border of pink polka dots.
Cut ribbon in lengths to wrap around the bottom borders of each cake. Secure with clear tape. If desired, embellish the top of the cake with some ribbon, also.