Proper Noun: The favorite, fictional submarine sandwich shop in the fictional Harry Potter universe.
Quizzlebee's does not actually exist in the Harry Potter novels or movies, but came into existence due to its overly English-sounding name and a certain, je ne sais quoi, that makes the reader instantly think of magic, Wizards, and disapparating.
Still don't believe in Quizzlebee's? Try to imagine Michael Caine saying it...
Harry Potter: While we're in Diagon Alley, we should stop in my favorite sub shop, Quizzlebee's!
Hagrid: What are you going to get, Harry?
Harry Potter: Either a roast beef with unicornraddish, or a dragon, lettuce, and tomato with cool, ranch dressing.
Hagrid: Aye, betwixt you and me I'd rather be subjected to the Cruciatus curse than eat at Quizzlebee's. I'll be outside, methinks.
Harry Potter: Here's 3 Galleons, go grab some greasy rubbish at Death Eaters (another fictional Harry Potter eatery).