sign own death warrant
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.
sign one's 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.