A fat lot of good, use, etc.
Definition 1 of 1

Sarcasm Indicator
Indicates speaker's disbelief in the usefulness or value of something, often with a tone of irony or sarcasm.

He brought in his old tools to fix the sink, but that did a fat lot of good.
Negative Outcome
Suggests an effort made with no positive results; something was done in vain.

I studied all week, and it did a fat lot of good on the test.
Emphasizes Failure
Highlights that someone's attempt to solve a problem has failed despite perhaps being expected to help.

She tried talking sense into him, but it was a fat lot of use.
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