Hold it to the light and sight along the handle. Then proceed to put all your weight into bending the spoon back the way it should be. In both instances, do not let any one see the handle of the spoon, because, of course, the spoon will not really be bent. You can play it up as much as you want to, apologizing profusely and insisting that you will pay for another spoon. Whatever you do, be sure to take into account the owners sense of humor.
Tricks are only fun if nobody gets upset.
To do the trick have the cup of the spoon down, grab the handle with one hand, and wrap your other hand around the hand holding the spoon. The handle will sweep out a wide arc behind your hand, but no will be able to see this. You must also remember to keep your hands upright, just as if you really were bending the spoon. It looks very realistic, especially if you get your pinkie to turn white as you press down.