"pull the plug"
Literally, this means to pull the plug of life support equipment and let someone die. Or less morbidly, unplug a bathtub and let the water drain out, ending the bath.
Metaphorically, it means to put an end to something:
- We've been more like roommate than lovers for the past 6 months. It's time to pull the plug on this relationship.
- I hate to pull the plug on this party, but it's midnight. I've gotta get some sleep.
There's also "pull the trigger" which has multiple connotations depending on context, but the same basic meaning of ending a period of waiting:
- Pull the trigger to kill/stop something "She's suffered long enough. You've just gotta pull the trigger and get it over with."
- Pull the trigger to initiate/start something (like a starter pistol at a race) "We're ready--just waiting on the boss to pull the trigger so we can start."
- Commit to a decision/action "Dude! It's not that complicated! Just pull the trigger and pick one!"