Place all 12 plastic cups on a baking sheet or on your serving plate, for easy transport. Leave the lids off the cups.
Cherry Layer
Place gelatin in a medium mixing bowl and pour cold water over the top. Stir and let sit for 2 minutes.
Once the gelatin has completely absorbed into the cold water, pour the boiling water over the gelatin and whisk until the gelatin is dissolved.
Add the grenadine and vodka. Whisk to combine.
Pour the grenadine mixture into the plastic cups, filling them about halfway full each.
Refrigerate for 45 mins to 1 hour, or until the jello is set.
Cola Layer
Place gelatin in a medium mixing bowl and pour cold cola over the top. Stir and let sit for 2 minutes.
Once the gelatin has completely absorbed into the cold cola, pour the boiling cola over the gelatin and whisk until the gelatin is dissolved.
Add the vodka and whisk to combine.
Pour the cola mixture into the plastic cups, filling the cups the rest of the way.
Refrigerate for 2 to 3 hours, or until the jello is set. Cover with plastic lids.
Notes
I recommend making the brown cola layer as soon as you put the cherry layer into the fridge. Once the cola layer is mixed and ready, let it sit out on the counter to cool down a bit so it doesn't melt the cherry layer when you add it in.