I’ve been watching a crime TV anime show lately, and I’ve run into this fancy and maybe offensive too ( sorry about that, if it is like so ) and to put you guys in the scene context here is a summary:
A rookie detective was assigned to save a hostage from a dangerous criminal, with the help of two subordinates, one of them is smart ( the star of the TV show ), and the other is old and wise. The team managed to box in the criminal and his victim. Now, our rookie detective and the old subordinate are pointing their high-technology guns ( only authorized individuals can use these types of guns ) toward the perpetrator.
The old subordinate: FREEZE !!
The criminal: STAY BACK !! DROP YOUR GUNS OR SHE DIES !!
The criminal unarmed the two, took a gun and screams while aiming at them: DIE!! ( and he pulls the trigger, but it’s not working ).
Our star showed up and killed him.Everybody is surprised, and after a while, the old subordinate said: Using an old man and a rookie as a decoy !?! You got a pair of cold stainless steel balls, don’t you?
The smart subordinate: Whatever it takes to earn the paycheck pops.
What does he mean by saying “You got a pair of cold stainless steel balls”?
I know that “balls” could sometimes be used interchangeably with “courage” (correct me if I’m wrong), but I think this means that the person has a cold heart.
I think you’re putting a bit too much emphasis on the word “cold”. Although it could have some connotation of emotional coldness here, I wouldn’t say the overall sense of the expression emphasizes that the person has a cold heart.
I don’t think you’d ever hear “cold balls”, as in your title. The word “steel” is an essential element of the expression in the dialogue that you quote.
I would say this is a variant of an expression where a person is said to have large or tough balls (=testicles) as a way of describing courage (as you put it) or boldness or fearlessness. Basically, “steel balls” = metal balls = unusually tough balls = an unusually large amount of courage.
“Cold stainless” is an extra bit of description added before the word “steel”. There could be various reasons for using those particular words: it might be to add some reference to the “coldness” of the behavior being described here, but it could be to make the expression sound better or more striking. These kinds of expressions often get creatively modified from a basic format: e.g. I think “brass balls” is a more common form of the expression.