In act 2, scene 1, Polonius meets with a character named Reynaldo and pays him to follow Laertes abroad. He wants Reynaldo to do three things: deliver money and letters to Laertes, see if Laertes is behaving himself, and imply that Laertes has been indulging in foolish behavior (sleeping around, gambling, getting into fights, etc.) in order to discern whether or not he's actually been up to these things.
This scene has been interpreted in multiple different ways; it either illustrates the sinister and manipulative side of Polonius's character or proves that Polonius is a babbling pseudo-intellectual. In either instance, he's a control freak when it comes to his kids. He doesn't trust them to make the right decisions, so he's doing everything he can to make sure Laertes acts like a model son when he's out of Denmark. This dishonors Laertes, because it proves that his father does not trust him to act honorably abroad and even implies that Reynaldo should spread rumors about Laertes's alleged wayward behavior.
The passage you might be referencing is included below (from act 2, scene 1):
And in part him; but' you may say 'not well:
But, if't be he I mean, he's very wild;
Addicted so and so: and there put on him
What forgeries you do please; marry, none so rank
As may dishonour him; take heed of that;
But, sir, such wanton, wild and usual slips
As are companions noted and most known
To youth and liberty.