A cold cock used to be the slang for a thing you'd use to bludgeon someone... like a bottle or something. It got made into a verb when you hit someone with a cold cock... But then the term for the weapon sorta dropped down, and cold cocking ws just known as hitting someone. Also the term "to clock" someone has existed meaning largely the same thing. The two got combined.
But... technically...
To Clock someone and to Cold Cock someone are basically the same thing. But to Cold Clock someone is combining those two mistakenly. Who knows, in 20 years, the phrase will probably become cold clocking.
and it will wear baggy tights.