From Longman Dictionary of Contemporary Englishdo somebody an injusticedo somebody an injusticeCHARACTER/PERSONALITYto judge someone’s character or abilities unfairly To say that you are a poor cook is to do yourself an injustice. → injustice
Examples from the Corpus
do somebody an injustice• Cutting the benefits of war veterans would be doing them a great injustice.• But they do themselves an injustice.• Indeed, it may well serve to do some injustice and violence to the integrity of the substantive phenomena. 