Practical joke cocktails: freeze Mentos into the ice-cubes, add to Diet Coke drink
Wired's HOWTO wiki suggests freezing Mentos into ice cubes and then serving them in Diet Coke-based cocktails as a kind of timed practical joke (the cubes melt, and the drink turns into a volcano). Diet Coke is recommended "because it isn't sticky."
Mix an Exploding Drink (via Neatorama)
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