I've read that before, it's probably why I phrased it that way, but I've never seen that skit of it. I have so many questions, like why they're meeting in a diner and how they're having this conversation without already understanding the concept of flapping meat noises.

That said maybe they have highly sophisticated automatic disguises a la some sort of holographic star trek translator badges, so maybe we're seeing the disguises but they are a cloud of ionised gas and a vibrating rock respectively, and they're so accustomed to moving about unnoticed that a diner is as good a place as any.

But obviously the comedy works better in a diner so it's probably not worth breaking it down except to draw out all the absurdities. I love how the one guy thought his mid eastern dignitary outfit would be appropriate. Maybe they're drawing from limited data about human culture and they really thought this would be the most innocuous way to talk in secret, because that's how we do it in all of our noir films. That would explain the permanent obligatory cigarettes they both have.