1)when your drink sucks so much you need a coke(you don't mix it with anything, just a regular coke dude) that shouldn't be there so your able to gulp it down, secretly (as in nobody needs to know your drink sucks or may be your just a light drinker)
2)a coke that's not supposed to be there or your friends shouldn't know its there or why its there.
3)a coke that doesn't talk because cokes don't talk
girl: your drinking tequila? straight up? that's hardcore
guy: (damn it i shouldn't not have ordered pure tequila on a cup, its not even chilled! i need a silent coke!) yeah, i know right? this food is really good, could really use a soda, waiter could you fetch me a coke(silent coke)?