someone who is dumb and has an ass

A stupid person; it refers to the lack of surface area on an individual's brain. The general thought is that the more surface area (wrinkles, creases, etc.) a brain has, the smarter the person is. Conversely, a person with a smooth brain (no wrinkles) has less surface area and would therefore be stupid.

Noun

1. Someone who attempts to be a smartass but is too dumb to actually succeed.

2. Someone who holds a stupid, illegitimate or completely baseless opinion with a perplexing amount of self-righteousness.

a person/animal/other organism that does actions/things that are unfavorable and seen by others as stupid, it's also an insult to a person who is pea-brained.

Redism (that 70's show)
meaning stupid moron

A person who is both dumb and an ass at the same time. Contrast with "dumbass," which is a conjugate of the terms, thereby creating a new class of person. However, "dumb ass" confers a meaning by which a person is both embarassing to the human race and of below average intelligence.

A person is both stupid (e.g. dumb) while also stubbornly refusing to stop being stupid when asked (e.g. ass)