A person who acts stupid but is really smart but only when it is needed.
Lets say Bob goes to school and steals some cafeteria food, pretty stupid. But when he takes his Algebra final he makes a 100. This would be a jawmuncher.
This word is commonly used in middle and high school when talking about a friend that does stupid things outside of school but is smart inside of school.
slip of the tongue perhaps,
Those idiots who drive around in a ridiculously raised pick up truck, making a top heavy vehicle even more top heavy and unstable
A:*gah*
B: "Whats the matter"
A: This dam prickup is blinding me.
B: Stupid thing's, as if there lights weren't blinding enough as it is.