Corrected entry: Pay close attention to the scene in the airplane where Butthead is behind one of the flight attendants in the aisle as she is serving dinner. He says, "Hey, I got a beer, want some?" A split second later, we see Beavis rush the cockpit and scare the pilots. At this exact moment, we now see Butthead at the back of the plane with that same flight attendant (same hair, clothes, everything), only she is seated in one of the take off seats and reading a book. Even if for argument's sake, Butthead did walk to the back of the plane, that same flight attendant couldn't have been there.
Corrected entry: In the scene in the car going to the airport, Muddy explains that the boys are to get back a satchel for him. When he demostartes how big it is, the whiskey bottle in his hands magically disappears and reappears.