Cut the watermelon in half lengthwise and carefully scoop out the flesh from one half, leaving approximately 1/2 inch of red fruit attached to the rind to create a sturdy shell. Place the hollowed watermelon on a large serving tray or baking sheet and use rolled towels around it to keep it stable and level so the gelatin mixture won't spill. This prep work takes just a few minutes and ensures your final product will have an even gel set.

In a large mixing bowl, combine the red flavored gelatin and unflavored gelatin packets. Pour the boiling water over the dry gelatin and stir vigorously for about 2 minutes until all the gelatin is completely dissolved with no granules remaining. I like to let this cool for about 5 minutes before adding the vodka so it's just warm to the touch—this helps the alcohol integrate better without evaporating too much of the flavor.

Once the gelatin mixture has cooled slightly, add the vodka and fresh lime juice, stirring until fully combined. The lime juice adds a subtle brightness that complements the watermelon flavor and prevents the shots from being too sweet. Pour the mixture slowly into the hollowed watermelon shell, filling it nearly to the top.

Carefully transfer the filled watermelon on its tray to the refrigerator and let it chill for 3-4 hours until the gelatin is completely set and firm to the touch. The cold temperature will help the gel set properly while the flavors meld together.

Remove the watermelon from the refrigerator and use a sharp knife to cut it into slices or wedges, similar to how you would cut a regular watermelon. I recommend chilling your serving plates or glasses before placing the shots on them—this keeps the gelatin firmer and makes for a better presentation. Serve immediately and enjoy!