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.

for one of these GUTTER rats
you're transporting.
Game of Thrones Season 2, Episode 2

What's a GUTTER rat like you
doing with a sword?
Game of Thrones Season 1, Episode 10

You like it in the GUTTER, don't you?
Game of Thrones Season 4, Episode 5

I could piss in any GUTTER
and soak five of you.
Game of Thrones Season 4, Episode 4

these GUTTER rats belong
to the Night's Watch now.
Game of Thrones Season 2, Episode 2