Route/highway argument
The route/highway argument is similar to the pop/soda argument because it stems from a difference in regional dialects, but it's a bit more nuanced. It's less of an argument than a semantic difference.
On parts of the East Coast, people call highways "routes," but only in a specific context. They might call it "Route 495," but then they will refer to "Route 495" as a "highway" when saying something like, "I live just a few miles from the highway." Thus, unlike the pop/soda argument, the East Coasters agree with the West Coasters on what the thing itself should be called—"highway." It's just that when some East Coasters refer to one of these highways by its number, they say "Route ___."
By contrast, in the South (or the Southeast), references to highways by number have some variation. Three-digit highways (but not interstates) are usually designated only by number, such as 316 or 441. Two-digit highways (but not interstates) are usually designated by using the word "Highway" rather than "Route", as in "Highway 10". All state highways can also be designated by the name of the state, followed by the highway number, such as "Georgia 400" (also known as the "Alpharetta Autobahn"). Interstates, regardless of number of digits, are generally referred to as "I-__", such as "I-20" or "I-95". "Route" does not exist in the Southeast... and if it did, it would be pronounced such that it rhymed with "out" rather than with "boot".
In addition, in the Los Angeles area (if not all of southern California) there are what the locals call "freeways," which are essentially highways on performance enhancing drugs. They are all too big to be either a "highway" or a "route," making this argument completely irrelevant in that part of the country. As far as nomenclature however, Angelenos refer to their freeways simply by saying "The ___" such as "The 10" to refer to Interstate Highway 10 or "The 405," "The 101" etc...
See also the logic behind road numbers.