A stupid or ineffectual person.Now the great numpty is serving 28 days in prison after another act of Comedy Terrorism in which he chucked paint over a Turner Prize nominated artist....
For a few minutes I felt like a complete numpty, then I got into it.
Some numpty forgot to make the developing room light-tight so we're all getting fogged film.
Origin
1980s: origin uncertain, perhaps an alteration of numbskull, the ending perhaps remodelled on the pattern of Humpty Dumpty.