The fallacy of Kafka-trapping occurs when an arguer uses the denial of an accusation as proof of that very accusation. It is an attack upon one arguer by another, whereby the mere expression of disagreement is treated as evidence of being wrong. As such, it is both an ad hominem attack and an instance of begging the question, because the accusation is assumed already to be true in refuting the accused person's denial.

Franz Kafka

Here is an example:

Bill: I think you're an alcoholic, Jill.

Jill: I don't think so.

Bill: That's just what an alcoholic would say, so you're proving my point even more.

Another example:

Jan: You're not cooperative.

Dan: I don't agree.

Jan: See!

Jan's rhetorical technique would make it impossible for a truly cooperative person, when wrongly accused of being uncooperative, to put up a defense against the unjust accusation. There mere attempt to do so, in Jan's eyes, is proof of guilt.

Very frequently, the technique is used for hidden mental states that are difficult or impossible to prove, ranging over various attempts to defend oneself:

Dawn: You look down on cats as inferior to other pets. You're a cat-hater.

Eli: That's not true, I just have a bunch of hamsters already.

Dawn: Right, because you hate cats.

Eli: I have had cats in previous years.

Dawn: But then you got rid of them because you hate cats.

Eli: Here's a photo of me hugging a cat and smiling.

Dawn: A pose you no doubt held reluctantly for a few seconds, just to stage that photo, so that you can pretend you don't hate cats.

Eli: Dawn, I am telling you that I do not hate cats.

Dawn: Why do you have to go out of your way to assert that? Because you really hate them. If you did love them, it would go without saying.

Dawn is prepared to take any of Eli's denials as evidence of her thesis that Eli hates cats. Since hatred is an inner feeling which is hard to prove, Dawn can get away with pushing this for awhile -- until someone calls it out as fallacious.

Background: The fallacy is named after the famous novelist Franz Kafka, whose writings often featured a persecuted individual being subjected repeatedly to this fallacy.