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.

Do you think I'm an IDIOT?
Game of Thrones Season 2, Episode 8

(GRUNTS)
You IDIOT!
Vikings Season 1, Episode 3

Hey, he may be
an IDIOT, but at least
The Big Bang Theory Season 7, Episode 11

And I'm an IDIOT,
because I always believe guys like that.
The Big Bang Theory Season 1, Episode 6

Any IDIOT can buy armor.
Game of Thrones Season 2, Episode 2