For this trick you need a paper cup and a handkerchief, plus a table on which to perform your magic.
First, pass around the cup and the handkerchief so everybody can see they're quite ordinary. Sit behind the table. The table should have a tablecloth on it so people can't easily see beneath it.
Put the cup on the table near you, upside down. Place the handkerchief over the cup. Now lift up both with your hand and talk to people about how you're about to make the cup magically go right through the solid table. Tell them to watch the spot on the table where the cup will go through.
As you bring the handkerchief up, make sure you have it in your fingers so it is held on two sides (i.e. between your thumb and first finger, and between your fourth and fifth finger). Keep talking to the people as you bring the handkerchief slightly towards you. Keep it low enough that the handkerchief still touches the table.
When you get to your lap, let the cup fall into your lap quietly. Your fingers will still hold the handkerchief out so it appears the cup is still there. Now slam your hand down onto the table in a forward motion, so that if your viewers DID see some movement, they'll think it was just part of your hand starting to move downward. Voila, the cup isn't on the table any more! Pull it from your lap and show it around.