It's called refusal to use one's brain. The real difference between a smart person and a stupid person is not IQ, education level, etc. It's how one uses what one has.
Examples:
1. A person with a low IQ and education who uses his/her abilities for good and doesn't forget how to learn is smart.
2. A physics professor with a PhD who pulls out in front of an 80,000 lb. semi doing 50 mph with about one car length between is stupid. A DOT cop once told me that he witnessed this very thing happen. Somehow, the truck driver was able to use combination of braking, downshifting and steering to minimize the impact and the physics professor's injuries were not life threatening. Thankfully, there wasn't a lot of traffic or other potential hazards within the danger zone.