Can you find the mistakes?
Which one is it?
How good is your slang?
What's the difference?
Are you good at British English?
100

I think they're new puppy is cute!

They're is the answer, it should be: their.

100

My mom said that I need to (do / make) my homework before going outside.

Do, because "do" means "solve" or "complete".

100

What does "flex" mean?

It means: to show off

100

What's the difference between "polish" and "Polish"?

"Polish" means: from Poland, and "polish" means: to make shiny.

100

In British English, what does "sweets" mean?

It means: candies

200

Cody doesn't likes to watch horror movies.

Likes, because you're using the third person auxiliary, the verb stays in simple form.

200

My girlfriend gave (me / I) a ticket to a concert.

Me, because "I" does the action, and "me" receives the action.

200

What does "slay" mean?

It means: to do very well

200

What's the difference between "resume" and "resumé"?

"resume" means: to continue, and "resumé" means: a list of qualifications.
200

In British English, what does "crisps" mean?

It means: potato chips

300

My bestie and I have gone to Canada last year.

Last year is incorrect, because that phrase is from simple past, not present perfect.
300

My co-worker (told / said) me to not share gossip with the others.

Told, because "tell" has a recipient, and "say" is general.

300

What does "bet" mean?

It means: i agree

300

What's the difference between "bass" and "bass"

"bass" means: instrument that makes a low sound, and "bass" means: a type of fish.

300

In British English, what does "biscuits" mean?

It means: cookies

400

I can't do nothing wrong in life.

It can be either: "can't" or "nothing", because it's a double meaning, you need to eliminate one.

400

Hey, could I (borrow / lend) your phone charger for a bit?

Borrow, because "lend" is to give, and "borrow" is to take.

400

What does "no cap" mean?

It means: no lie, for real

400

What's the difference between "record" and "record"?

"record" means: physical or digital musical recording, and "record" to capture audio or video.
400

How do you pronounce "It's Tuesday isn't it?" with a British accent?

It's pronounced: It's chewsday innit?

500
Won't you invite me to your party next month?

Won't is the mistake, since it's a question, all questions need to be in neutral, or in this case, put it as a question tag.

500

What I like to do for fun is (see / watch) romcoms and (listen / hear) to k-pop.

Listen and watch, because "hear and see" is a simple ability, and "listen and watch" is an activity.

500

What does "ghost" mean?

It means: to stop communication abruptly

500

What's the difference between "permit" and "permit"?

"permit" means: to give permission, and "permit" means: document of allowance

500

How do you pronounce: "bottle of water" in British Accent?

It's pronounced: bo'oh'o'wo'ah