A food reviewer at a website called The Takeout realized that a Wendy's Frosty might be even better if you dumped some BOOZE into it. So she bought a bunch of liquors and a bunch of Frostys and tested out how they taste together.
And the top two are: Kahlua and Baileys Espresso Cream. I guess neither of those are surprising, since they're both key ingredients in most of the drinks that fall into the "alcoholic milkshake" category.
The rest of the good options are: Rumple Minze peppermint schnapps . . . Godiva Milk Chocolate liqueur . . . and Frangelico.
The liquors that didn't taste good are: Godiva White Chocolate . . . Captain Morgan Spiced Rum . . . Smirnoff Vanilla Vodka . . . and Rumchata.
And the liquors that made her feel like GAGGING when they were mixed with a Frosty are: Fernet Branca . . . Canadian Club whiskey . . . and Smirnoff Whipped Cream Vodka.