A person who is so ignorant or stupid that he/she is clearly "Operating On Brain Stem Only" --OOBSO-- with no higher brain activity.
1. The clerk in any American store who does everything by rote and, if asked a question even slightly out of the expected, is totally unable to respond.
Clearly an OOBSO.
2. George W. Bush, OOBSO extraordinaire.
3. Loud mouth fools on talk radio, OOBSO paradise.
4. Sarah Palin, Brain Baked Alaskan OOBSO.