sign (one's) own death warrant

To knowingly do something that will bring one trouble, punishment, or harm (and perhaps literally one's death). If you stay out past curfew again, you know you're signing your own death warrant, right? Testifying against the mob boss is like signing your own death warrant.

Fig. to do something (knowingly) that will most likely result in severe trouble. (As if one were ordering one's own execution.) I wouldn't ever gamble a large sum of money. That would be signing my own death warrant. The killer signed his own death warrant when he walked into the police station and gave himself up.

Bring about one's own downfall, do oneself irreparable harm, as in In taking his secretary to a risqué nightclub, the parish priest was signing his own death warrant . This expression may refer to acts that ensure someone's later murder, as when, in 1921, the Irish revolutionary leader Michael Collins signed the peace treaty he had negotiated with England and said, "I tell you, I have signed my death warrant." Thirteen months later Collins was assassinated by political opponents. The expression is also used hyperbolically, however, for severe repercussions or punishments. [First half of 1900s] Also see shoot oneself in the foot.