In reality, it is inadvisable to wear two condoms simultaneously.  This applies whether it's two male condoms, worn one on top of the other, or if it's a man wearing a male condom whilst his partner wears a female condom.  Friction generated when the two condoms rub together increases the possibility of abrasion, tearing, or slippage of both condoms, making transmission of bodily fluids more likely than if only one condom had been used.  Even if you're using lubricant, one condom is safer than two.

And as we all know, boys and girls, you're better safe than sorry.