An honest response to an accusation should be constructive. One way to achieve that is to express empathy, question,break down broad terms(if any) into specific instances and address each of them.
But in some instances you don't want spend your time and energy because it's not important to you.
Jack: Earth is flat
Jill: that's not true
Jack: oh really, prove it
Jack: (with friendly tone) you're smart, you do nothing at office but still manage to keep your job
Jill: ' that's not true'
or 'what makes you think that'
Jill may also reply cleverly with wit/humor and disarm attack, however let's assume Jill is too tired for it.
Jack: okay, if not why don't you tell us what you did today?
Jill has sound reasons to back herself in both cases but she will be owning the burden of proof and in second example even giving weight to the accusation, appear defensive and exposed herself to be scrutinized on details endlessly. Answering 2nd question is also condescending and handing some authority to Jack.
In conclusion, can we formulate a strategy to avoid owning burden of proof or turning it around on them.