Where in the play is there evidence of Hamlet being funny? It might be in act 4, scence 4.

Hamlet's humor is of a sarcastic nature.  He is sarcastic with Polonius in Act 2, Sc. 2 when Polonius is attempting to draw out of Hamlet the reason for his depression.  Hamlet, naturally, sees through Polonius's attempt and speaks in riddles and double meanings.  Also, in Act 4, Sc. 2 when Hamlet speaks with Rosencrantz and Guildenstern about the location of Polonius's body, he again speaks in riddles and double meanings.  Additionally, there are many instances sprinkled throughout the play where Hamlet gets in a good zinger.