The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

Why so GLUM, chum?
The Big Bang Theory Season 4, Episode 18

Oh, is that why
you're so fucking GLUM, hey?
Game of Thrones Season 7, Episode 4