From Longman Dictionary of Contemporary Englishknow full/perfectly wellknow full/perfectly wellREALIZEused to say that someone does know something even though they are behaving as if they do not You know full well what I mean. → well
Examples from the Corpus
know full/perfectly well• Oh, I glory in inconsistencies, as you know full well.• She knew perfectly well he didn't trust her.• You know perfectly well I can't.• Ought we to think less of Johnson for agreeing because he knew full well that he could influence Boswell?• I know perfectly well that metastases are not just a characteristic of malignant cells, spreading from organ to organ.• The public know full well that the Labour party taxes and spends, taxes and spends.• You know perfectly well that women get depressed at - at certain times.• In everyday life we talk about things being good and bad, and we know perfectly well what we mean. 