loose cannon

plural loose cannons

1. nauticalA cannon that breaks loose from its moorings on a ship during battle or storm, with the potential to cause serious damage to the ship and her crew.
2. broadlyidiomaticAn uncontrolled or unpredictable person, especially considered liable to cause unintentional or indiscriminate damage.

   Jack is considered a loose cannon due to his volatile personality and his track record of being unable to maintain his composure.

   2 more examples

   Sooner or later this party gets busted and all your friends stumble back home But you're the loose cannon who could never be trusted so you'll hide from the cops all alone.

   2013, “Post Party Depression”, in Rogue Taxidermy, performed by Days N' Daze

   Even in MAGA circles, Loomer is regarded as a loose cannon who loves to get attention from inflammatory comments that undermine the Republican Party.

   2024 September 13, Jeet Heer, “How Donald Trump Got Loomered”, in The Nation, archived from the original on 05 Oct 2024

present singular third person loose cannons · participle present loose cannoning · participle past loose cannoned · past loose cannoned

1. idiomaticintransitiveTo behave in a way such as to cause unintentional or indiscriminate damage.

   Gerald's loose cannoning triggered a volley of faithfully quoted media coverage which blasted a hole in his company's profits […]

   2006, Gerry McCusker, Public Relations Disasters: Talespin--Inside Stories and Lessons Learnt, page 179