The girl seems interested in what's going on at his end of the bar; she gets off her stool and meanders over and reads the napkins.
Max reads the napkins, and processes them exactly enough to notice that they are being used to communicate with him. He does not process them any more than it takes for him to shout "NAPKINS! You're- NAPKINS! NO!"
"Weird," says the girl. "Okay, where is this place?"
It's called Milliways.
The girl offers Max this napkin once she's read it.
"No, you're not! You're- those are- you can't do that! That's not- no!"
He stares at the "It's called Milliways" napkin, in the absence of anything else that suggests investigation. Alarm is not receding, but mounting as more seconds tick by without any explanation clicking into place.
"What's going on?! Where's Brenda's? What did you do?!"
"I didn't do anything!" exclaims the girl. "I walked in here same as you!"
"I was talking to the bar, not y- I was talking to the bar, jesus christ, the- how do you "appropriate the door", why would- what do you need the door for?" His eyes frantically scan the countertop for another napkin.
"Are we stuck?" asks the girl.
No, of course not. When you open the door it will return you when and where you left.
He ignores the thing about being able to return home. The universe contains magic door-stealing talking bars, which is orders of magnitude more important than whatever he had planned for that that. And the way these napkins are talking, he's going to have to work at getting any answers.
"What do you mean you couldn't begin to tell us? Where did you come from, then? Who installed the magic talking napkin bar, huh?"
"So there's the door thing, and there's you, and you're separate, and you do napkins and beverages, and somebody else - invites people over to partake?" says the girl.
That's about the size of it. I can produce things other than beverages, though.
He looks at the other napkin, and growls "...things other than beverages, well that explains everything..." under his breath.
Her, please.
"At her," corrects the girl. "Things other than beverages like what?"
Virtually any medium-sized nonmagical object, although I do have to charge your tab appropriately.
He snatches the new napkin from the counter.
"Our TAB?! Any- nonmagical?! As opposed to- as opposed to...!!!"
Max would like to get properly riled up about the magic thing, but for some reason he's stuck on the possibility that he might be charged for being here.
"She's being nice so you shouldn't be mean," corrects the girl. "So I could get my Pokéballs and Potions here?" she asks the bar.
Yes, although I cannot guarantee that I can offer them at a competitive price depending on whether your usual establishment is having a sale or offers other discounts.
"Wh- okay, we're back to this. The Pokémon thing. I'm led to believe that's not a real thing. I was also led to believe magic bars weren't a real thing, though, so if you don't mind clearing that up..."
"What, really? You weren't just randomly being a jerk, you actually don't know what Pokémon are?" says the girl. She pulls one of the Pokéballs off her belt, expands it to full apple size, and bounces it on the floor. It opens, there is a flash of red light, it closes and bounces back to her hand, and where it struck is a creature.
"Th-that's a goddamn Zigzagoon! How did you- where did you...?"
The girl puts the creature's Pokéball on her belt again, then picks the animal up and puts it on her lap. It curls up there happily and nuzzles her under the chin. "He used to be a Zigzagoon but now he's evolved," she says. "I thought you didn't think Pokémon were real, how did you even get that close?"
There's got to be a connection, somehow. He should have paid more attention to his kid's yammering about it... no, no, he shouldn't have, that wouldn't have been a reasonable decision given what he knew at the time. Still...
"Oooone," agrees the critter.
"And I already told you why I don't think a Pokémon made the bar!"
"Pokemon is... its a video game, my kid used to play it, it was... you caught monsters and they fought each other, or something, trying to get batches of something. Supposedly completely fiction! Not a physically possible thing! This... has that in common with that thing. The bar thing, also impossible. There probably aren't multiple kinds of impossible coincidentally happening at the same time. So... connection! What is it?!"
The door can lead to arbitrary different worlds, including those from which the two of you came.
"You do NOT lie to me! Do NOT tell me lies right now!"
Different worlds, that's... even in the face of the windows, and the napkins, and the thing that isn't a Zigzagoon, this... isn't right. Not if different worlds can mean things like... like that. Something else has to be going on here.
The girl collects previous napkins into a stack and reads through them, then pulls out a notebook and starts transcribing them.