The demonym “Glaswegian” comes, linguists think, as an analogy of the Irish city of Galway. “Glasgow” and “Galway” are two fairly similar looking words. And Galway has long had its own analogy with another similar-looking word: Norway. Galway’s demonym is “Galwegian,” as an analogy of “Norwegian.” So “Glaswegian” is a sort of a photocopy-of-a-photocopy of Norwegian. Not something anyone could ever guess!
Another good one is Glasgow -> Glaswegians. Here’s a pretty interesting article about a few odd demonyms:
https://www.atlasobscura.com/articles/demonyms-linguistics-nicknames