[Alhaitham does indeed know what housewarming means, thank you very much, but he also knows (assumes) that it is just an excuse for what Kaveh really wants to do.]

Do you not already have people to go and be merry with if you want to? You certainly had a lot of fun with that Fontanian last time.

[Because clearly Kaveh is only doing all this to get some company that isn't just Alhaitham, right? He's well aware of how much his senior is unable to tolerate him for long periods of time and always needs some kind of escape, so clearly this is what he has resorted to this time.]