be the exception that proves the rule

be the exception that proves the rule

To contradict a rule and thus confirm that the rule exists. A: "We're always told to get eight hours of sleep, but I usually feel really groggy when I sleep that much." B: "Well, I guess you're the exception that proves the rule."
See also: exception, prove, rule

be the exception that proves the rule

if you say something is the exception that proves the rule, you mean that although it does not support the statement you have made, the statement is usually true This woman is the exception that proves the rule that it is impossible to be a warmonger and a feminist at the same time.
See also: exception, prove, rule