In Act I, Scene III of Shakespeare's Hamlet, there is one source of humor. When Laertes is preaching to the young Ophelia, he is very strict in his instructions. Laertes is very serious and straight forward with Ophelia. Laertes warns Ophelia not to lose her innocence with someone like Hamlet. He warns Ophelia that Hamlet has to choose a wife with which the state will be pleased. Hamlet has responsibilities as the Prince of Denmark.
Truly, Laertes goes on and on about how Ophelia should not trust Hamlet. He warns her to not lose her innocence with such a man. He warns her that Hamlet may only be toying with her emotions. No doubt, Laertes preaches a long sermon and appears to be most holy in his speech.
The humor is shown in Ophelia's response to her dear brother. She seems to be absorbing everything Laertes has preached to her. Then she responds in a humorous manner. She tells Laertes that he is good at preaching about what she should do, but he himself does not practice what he preaches:
I shall keep the purpose of this good lesson
As watchman to my heart. But, my good brother,
Don’t, as some insincere ministers do,
Show me the steep and thorny way to heaven,
While, like a proud and reckless wild man,
Preaches against the primrose path of sin
And does not practice what he preaches.
It is quite humorous when Ophelia points out that Laertes is as an insincere minister. He does not mind instructing Ophelia in chaste behavior, but is yet to actually follow his own instructions. Touche for Ophelia. She seems competent enough to handle herself. Of course, her brother means well, even if he is a hypocrite.