Dictionary.com defines STUPID as:
1. lacking ordinary quickness and keenness of mind; dull.
2. characterized by or proceeding from mental dullness; foolish; senseless: a stupid question.
3. tediously dull, esp. due to lack of meaning or sense; inane; pointless: a stupid party.
4. annoying or irritating; troublesome: Turn off that stupid radio.
5. in a state of stupor; stupefied: stupid from fatigue.
6. Slang. excellent; terrific.
7. Informal. a stupid person.
You may have encountered individuals who may fit that description. It may be a temporary state of stupidity (as most of us go through that phase); or it may be a permanent state.
What do you do to them? Ship them off to the Island of Stupid. (Click the image to enlarge.)

Have you ever met someone who...
- Asks the same question over and over again?
- Asks for advice and comes off all-knowing? -- "I already know how to do that." Well, duh, I didn't say you didn't know that. Practice makes perfect. If you are getting problems with the results then you are not doing it right.
- Asks a question right after someone else asked that same question -- and it was already answered?
- Keeps using their cellphone (holding it to their ear) while driving even after the CA law was already passed?
- Doesn't use their blinker when changing lanes?
- Doesn't look when they are backing up their car?
...the list can go on. Common sense may be relative, and so is being stupid. A stupid act may result from an 'inconsiderate' act or from some random comment that should not have been made. If that person drives you nuts, buy a ticket. Make sure s/he goes on that trip to the Island of Stupid. If not, you'll just have to accept the fact that stupid is everywhere.
All aboard!