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.

...than some complete IDIOT.
Breaking Bad Season 3, Episode 12

Look at this IDIOT!
One ball and no brains.
Game of Thrones Season 1, Episode 5

Who's an IDIOT?
Game of Thrones Season 7, Episode 7

Yeah. Like you're an IDIOT.
Breaking Bad Season 5, Episode 14

- I feel like an IDIOT.
- No, come on, you're not an IDIOT.
The Big Bang Theory Season 5, Episode 17