off the deep end vs quicksilver

off the deep end

• Crazy, erratic, or irrational. 

• Extremely angry. 

quicksilver

• Unpredictable, erratic or fickle; mercurial. 

• The metal mercury. 

• An amalgam of mercury and tin applied to the backs of mirrors, quicksilvering. 

• To overlay with quicksilver. 

• To treat with quicksilver.