What is it called when you use someone's exact words against them?

Solution 1:

There are a number of expressions that suggest using a person's own words, methods, or weapons against them.

• Giving them a taste of their own medicine

This means doing to someone what they have either done to you or are known to do.

• Poetic justice

This means that a person's end or punishment was fitting for their actions.

• Turning the tables

Not so much using someone's weapon against them, but reversing fortunes, perhaps turning a disadvantage someone gave you into an advantage against them.

• Comeuppance

This simply means that a person received "what was coming to them"; that unpleasant words or behaviour resulted in the most likely or expected unpleasant outcome.

Perhaps less so:

• Give someone enough rope to hang himself

A slightly different angle, but this means to allow someone to bring about their own downfall.

• They backed themselves into a corner

This means that the person by their own careless words got themselves into difficulty or lost an argument.

Depending on how you are using this, I thought it might also be worth suggesting that such a situation, where somebody is beaten by their own words, may be an example of irony. To be a true example of irony, the result must be the reverse of what was to be expected. So, if a person said something expecting his statement to win an argument, but his words actually caused his downfall, this would fit.