This seems like a lie. In fact, it’s hard to imagine a way that it is not. Is there any way that he really laughed about the player’s approach at just that moment? He listened to that whole speech about what a piece of work man is and then suddenly thought, “Oh! We saw the players on the way here. If Hamlet is so undelighted with man, he’s going to be a real dick to those actors when they get here. Isn’t that funny?”
The closer I look, the more distinctions there are between Rosencrantz and Guildenstern. They’re played like they’re twins. And Stoppard’s play heightens the effect that they can’t keep their identities straight. But I’m looking at a page of text right now and on it, I see a lot of back and forth between Hamlet and Rosencrantz with only one (rather important) line from Guildenstern. Guildenstern doesn’t speak much but when he does, he tells the truth that Hamlet’s been asking for.
It makes me wonder about Guildenstern. Has he been sort of swept up in Rosencrantz’s wake? If he’d been on his own, could he have actually been a friend to Hamlet? Or is he just a quieter character? Less skilled at lying, maybe but just as guileful. There’s no indication that he laughs when Rosencrantz does in this “man delights not me” section. But then, there’s also no indication that he doesn’t. You’d have more lines if you played Rosencrantz but you’d have a lot of interesting decisions to make if you played Guildenstern. How allied with Rosencrantz is he? Is he silent here because he’s conflicted? Or stupid? Or distracted? Or afraid to implicate himself? There is so much potentiality in silence.