rattle (one's) saber
To make aggressive, blustering, and typically empty threats. I'd like to think that his threats are just him rattling his saber, but I'm not too sure anymore. The boss just likes to rattle her saber every now and then to make herself feel powerful.
rattle one's saber
and rattle its saberFig. to make threatening statements or actions. The president is just rattling his saber. He would never attack such a small country!