Super Clown of Smallville - S1.E6

A wealthy old man promises to give a large amount of money to anyone who can make him laugh. Clark Kent and Krypto attempt to make him laugh but fail miserably. Later, however, Clark must reveal himself as Superboy to the old man in order to save an airplane that is about to crash. The old man begins to laugh because he thinks that the idea that Clark Kent wants him to believe that he is Superboy is hilarious.