The dry, albeit stiffly correct, Merriam-Webster Dictionary, defines a cocktail as "an iced drink of wine or distilled liquor mixed with flavoring ingredients." Clearly, that's an incredibly broad definition, but it does reflect the most modern notion that pretty much any mixed drink is a cocktail
So now days, the word has come to mean almost any mixed drink that has alcohol in it. A cocktail today usually contains one or more kinds of spirit and one or more mixers, such as soda or fruit juice. Additional ingredients can include ice, sugar, honey, milk, cream, liqueurs, fruits, and various herbs.
So for what it's worth, Skol vodka and Kool-Aid could be construed as a cocktail. We here at Imbibing Culture frown on that though.