Brumate Glitter Flask
Summer is boozin' in the park season. Summer is bachelorette season. And I'm pretty sure every season is Glitter Champagne, Glitter Mermaid, and Glitter Maleficent season, so getting a Brumate Glitter Flask as a gift for your girlfriend is both a win now, and a win forevermore.
Unless your girlfriend is actually your ex-girlfriend Karen, in which case I recommend this type of glitter over the holographic spirit flask kind.