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.

All you can say with absolute certainty
is that that JOKE is not funny here.
The Big Bang Theory Season 1, Episode 11

All right, I cared enough to memorize
that stupid JOKE, but that's all I care.
The Big Bang Theory Season 2, Episode 19

I've wasted
all your money. It was all a JOKE.
Vikings Season 1, Episode 1

It was a JOKE.
Vikings Season 1, Episode 7

What? It's a JOKE.
The Big Bang Theory Season 7, Episode 15