What word (or expression) can I use that means “to break someone's lie”?
I mean to aggressively point out that she or he is lying.
She stood up and ___ his lie/that he was a liar.
I'm thinking of debunk, but it doesn't seem suitable here.
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Consider "to call someone's lie":
There are times when a subject may try to misinform you, even utter lies. In such cases, you don’t have to call his lie.
Another possibility was suggested in the comments: to call someone out (on their lie.)
I didn't get mad, but could tell he was lying and later called him out on it.
Also to call someone on their lie can be used (omitting the preposition "out"):
Why did my boyfriend get so mad when I exposed his lies?
So, why did your ex-boyfriend get so angry when you called him on his lies?
(In the example above, the first line is a question, and the second is part of the answer restating the question in different words. I highlighted "expose" and "call out on" in bold to demonstrate parallelism. To show they mean the same thing.)
to prove a statement, opinion, or belief to be wrong or false
"She stood up and refuted his lie."
She stood up and denounced him as a liar or She stood up and denounced his lies.
You could even say I denounce you as a liar! or just You liar! or You lie!
When said strongly, additional words aren't really needed.
From Merriam-Webster (www.merriam-webster.com/dictionary/denounce):
1 : to pronounce especially publicly to be blameworthy or evil
And less so, but related:
3 : to inform against : accuse
The word decry was mentioned, and is possible, but to me is not quite right, because that is (Merriam Webster) express strong disapproval of which isn't quite the same as saying that someone is lying/wrong/etc. (The person could be telling the truth and you still decry him.)
You could give him the lie
To charge with falsehood; as, the man gave him the lie. [Webster's]
The first word that came to mind for me was: busted! Growing up in Southern California this was a term I heard all the time when someone was exposed as a liar.
Similar to give him the lie, you can give the lie to [something].
She stood up and gave the lie to his claims
I would say something like this:
She stood up and called him out on his lie. She stood up and put him on blast for his lie.
Another good word would be 'refute'. It's similar to 'debunked', which you had mentioned.
Refute: prove (a statement or theory) to be wrong or false; disprove.
You could also use 'challenged' which is less assertive, or invalidate(d).