That clacker kept talking nonstop during the meeting, and no one could get a word in.

clacker 是由动词 clack（发出咔嗒声、喋喋不休）加上后缀 -er 构成的名词，指"不断发出噪音的人或物"，在这里比喻"喋喋不休的人"。clack 本身模仿物体碰撞的声响，引申为"说个不停"。