Legally speaking, this is probably okay, barring any specific circumstances that may arise from either your jurisdiction, platform terms of service, et cetera. You should absolutely consult a lawyer to discuss the specific case you are envisioning, as there may be regulations about what you can do without user consent in force, as well as rules about how you need to market your application if it can, effectively, navigate to arbitrary URLs (see below).
Regardless of the legal issues, this seems like a phenomenally bad idea. If you don't control the URL you're navigating too, you are delegating some aspect of your product's experience to a third party that has no interest or obligation to support you. The entity with control over the URL could see all this traffic coming from your product, not like it (or just be a troll) and choose to change the content of that URL to something far less amusing. You still bear the responsibility for displaying the content at that URL, even if it is no longer what it was when you shipped the game.
If you do control the content of the URL, you're back in the legal arena (making sure you have the rights to the content at the URL for the use you are applying).
It also seems like a joke in pretty bad taste, especially at this point, as well as an unpleasant user experience overall.