An individual with little or no understanding of a subject, who may find it difficult to learn by experience e.g. "See you? Ye're a grade-wan numpty - flyin' colours, nae kiddin'!"
Tony Blair (particularly with regard to his understanding of the UK electorate)
"Dubya" Bush (for his services to Play Station sales)
a) Someone who (sometimes unwittingly) by speech or action demonstrates a lack of knowledge or misconception of a particular subject or situation to the amusement of others.
b) A good humoured admonition, a term of endearment
c) A reckless, absent minded or unwise person
b) i.e. "Silly billy", "You big dafty"
c) "That numpty's driving with no lights on!"