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.

Who cares about your stupid dancing TEACHER?
I can't go.
Game of Thrones Season 1, Episode 6

If you're interested in making
a sincere effort to be a good TEACHER...
The Big Bang Theory Season 8, Episode 2

Well, you're a wonderful TEACHER.
Game of Thrones Season 5, Episode 2

...and one particularly persistent
PE TEACHER...
The Big Bang Theory Season 4, Episode 2

high school science TEACHER
Mr. Hubert Givens..."Sheldon, Sheldon.
The Big Bang Theory Season 12, Episode 23