twelve rocks in a box
a jury. You, and eleven of your fellow citizens if you've ever served jury duty. Derogatory, may be used by defense or prosecution counsel if you came back with a verdict that went against them.
"The guy had a .15 BAC, hit a parked car, and puked on the officer, but those twelve rocks in a box came back with a "Not Guilty". Can you believe it? I need to do insurance law..."