Retortion
Retortion is the act of identifying a self-referential contradiction in an opponent's position.
So, for example, if I were to write, "No one can type a coherent sentence in English," a thoughtful critic might retort: "But what you just wrote provides evidence against what you claim to be true."
Retortion is spelled "retorsion" in French. The idea of turning an opponent's self-referential contradictions into a reason for rejecting the position is common among Transcendental Thomists, who used various forms of this argument to demonstrate the instability of Kant's epistemology.