It's true. The yellow dye in Mountain Dew is a component in a few spermicides. Essentially, you'd have to drink gallons of it, and you'd replenish it in a matter of hours. It's not like your your mom shrinks.
I voted Pepsi, just because Captain Morgan + Pepsi = Win. I don't like it with Coke. Although, I will drink both on any occasion, really.