Prepare the caramel sauce by combining sugar, corn syrup, water, cocoa powder, and salt in a saucepan over medium heat. Do not stir; swirl occasionally until it bubbles.
Continue cooking until it reaches the soft-crack stage (270°F) or forms a firm ball in ice water.
Remove from heat; stir in red food coloring, butter, and vanilla until smooth.
Pop the popcorn using an air popper and remove unpopped kernels.
Spread popcorn on a baking sheet; drizzle warm caramel over it.
Toss gently to coat evenly; cool completely before breaking apart into pieces.