I love big damn movies like this, you take the midwits that are Beavis and Butt-Head, put them in a cross-country road movie involving biological weapons and the FBI and just let the comedy flow forth. But honestly, who cares about the plot? It's all about the pair causing havok on a plane, freaking out in the desert on peyote and the military going full DEFCON 4 after Beavis prank calls them from the oval office. The jokes are incredibly…