What do you bet,? Want a bet? , What do you say?
If someone is showing off and you mean , you don't know that much can you say.:
whatdo you bet you don't know this?
Do you want to bet something?

I'd like the colloquial way of saying it please

Thank you

Question

What do you bet,? Want a bet? , What do you say?
If someone is showing off and you mean , you don't know that much can you say.:
whatdo you bet you don't know this?
Do you want to bet something?

I'd like the colloquial way of saying it please

Thank you

Answer

What do you want to bet that you don't know what you are talking about?
I'd bet even money that you don't know what you are talking about!

When you think you hear 'want a bet' you are really hearing 'wanna bet' = want to bet.

If you want to go even more colloquial, you can say 'you are talking s***, you know that?' (that means, it's nonsense what they are saying, or it is wrong)