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.

But I don't want to know
how many UNDERPANTS you own.
The Big Bang Theory Season 7, Episode 1

Uh, no. We lock that door,
lower our UNDERPANTS a little,
The Big Bang Theory Season 10, Episode 8

Instead of UNDERPANTS, I covered
my crotch with potato salad. Thoughts?
The Big Bang Theory Season 3, Episode 15

"Leonard will restrict video gaming
in UNDERPANTS to hours Penny is not home.
The Big Bang Theory Season 10, Episode 13

because you no longer
wear UNDERPANTS.
The Big Bang Theory Season 5, Episode 4