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.

Oh. 'Kay.
But you're being pretty RUDE.
The Big Bang Theory Season 11, Episode 16

if a customer's being RUDE.
Breaking Bad Season 4, Episode 8

I agree, it's RUDE,
but she asked for privacy.
The Big Bang Theory Season 3, Episode 10

He was condescending
to me, RUDE about you,
and l do not like him.
Breaking Bad Season 4, Episode 3

Listen, I don't
want to be RUDE,
The Big Bang Theory Season 5, Episode 2