Dickhead

"Dickhead is a slang and derogatory term for a stupid person. It is usually only applied to men because of 'dick' being slang for penis, and this meaning and usage is first cited from the 1960s, but the practice of using the word ‘head’ as a suffix is much older, as in 'fathead', 'meathead' etc, which are also derogatory terms used to describe stupid people and they date from the mid-19th century. There is another theory about the etymology of 'dickhead' that derives from the German dick meaning 'fat' or 'thick', which has no connection with the more modern version of 'dickhead' that derives from the slang for penis. There is evidence that this less derogatory version is also much older, and dates from the mid-19th century."