We've all seen the video of the wedding cake destroyed by a clumsy waiter at the reception. People just expect it. This can be dangerous, of course, because an angry bride can easily kill thirty men bare handed. It's a different story when the bride is in on the destruction.
If the bride and groom agree to pull a prank, the guests will be shocked and amazed and they will tell the story for generations. The trick, as mentioned, is that the bride must to be in on it. The other trick is to perform the prank with a fake cake and then have the real wedding cake waiting in the wings.
The most obvious wedding cake pranks involve balloons. For the first, you make a cake that is actually a couple of helium filled balloons. Using the lightest weight of frosting you can find, decorate the balloon cake to look like a real wedding cake. The person carrying it pantomimes carrying a heavy cake with extreme care and concern. When this porter approaches the bridal table, he feigns tripping and releases the cake which rises up. This is particularly spectacular if the reception is held out doors because the cake just keeps rising upward.
The second prank doesn't necessarily need the groom's foreknowledge, just the bride's. Again, make a cake of balloons, but these don't need helium. Before inflating the balloons, put a small amount of whipped creme inside the balloons. Decorate the cake with a light frosting. Make sure the balloons are tied really well to the tray where the "cake" is supposed to sit.
The next part relies on the fact that the groom is usually the closest to the cake when it gets cut. Make sure that the cutting knife has a sharp point. When the groom pokes some part of the cake, the balloon will pop sending frosting all over. If things go particularly well, the balloon will make a loud pop.
Most other wedding cake pranks aren't as practical or are illegal. For example, most laws prohibit putting hallucinogens into food products. It is also a bad idea to hollow out the center of a cake so you can hide some slightly drugged squirrels that wake up just before the cake is cut.
Whatever you choose to do, be safe and have fun. Remember the most important safety rule: If you make the bride angry she will kill you in an unpleasant way.
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