From Longman Dictionary of Contemporary Englishbe your own worst enemybe your own worst enemyPROBLEMto behave in a way that causes problems for yourself → enemy
Examples from the Corpus
be your own worst enemy• My father was his own worst enemy.• Many drivers are their own worst enemy -- driving too close, driving too fast, all the usual faults.• You could say that Gilly is her own worst enemy.• My mother was her own worst enemy. She knew she was ill but she did nothing to help herself.• People are their own worst enemies.• To what extent would she say she was her own worst enemy?• Players can be real snobs about names, too, so they are their own worst enemies.• In other words, we are our own worst enemy.be your own worst enemybe your own worst enemyHARM/BE BAD FORto cause a lot of problems for yourself because of your own behaviour → worstExamples from the Corpus
be your own worst enemy• In other words, we are our own worst enemy.• My father was his own worst enemy.• People are their own worst enemies.• Players can be real snobs about names, too, so they are their own worst enemies.• To what extent would she say she was her own worst enemy?• You could say that Gilly is her own worst enemy. 