https://www.logicallyfallacious.com/logicalfallacies/Shifting-of-the-Burden-of-Proof

Shifting of the Burden of Proof

onus probandi

(also known as: burden of proof [general concept], burden of proof fallacy, misplaced burden of proof, shifting the burden of proof)

Description: Making a claim that needs justification, then demanding that the opponent justifies the opposite of the claim. The burden of proof is a legal and philosophical concept with differences in each domain. In everyday debate, the burden of proof typically lies with the person making the claim, but it can also lie with the person denying a well-established fact or theory.

Example #1:

Jack: I have tiny, invisible unicorns living in my anus.

Nick: How do you figure?

Jack: Can you prove that I don't?

Nick: No.

Jack: Then I do.