Do you know the oldest gag in the book? Or at least the oldest gag since Diet Coke and Mentos were born. This quick video tutorial will have you testing this out every time you have Mentos and Diet Coke in your hands. Just let thirteen Mentos slide quickly into the Diet Coke and watch the eruption, just like Old Faithful. Now, try and screw a cap on it for the perfect prank. Use this as inspiration for one of your April Fools Day pranks!