"Dickhead" was a word coined at least 100 years ago but less than 1,000,000 years ago in some far away land. It is a composition of the words "Dick" and "Head" and if you didn't already realise that you're a dickhead.
There are many different types of Dickheads and the word is is used as a general insult. It implies that either the person thinks with their dick as opposed to their brain or that they have a dick on their head. Either one of these stupid origins can be used but mostly nobody gives a shit what the origin is otherwise they would be too confused to use it.
Even though a dick is usually located on a male, dickhead can be used to pwn bitches who are just plain fucktards. This unimaginative and overly general word is interchangeable with practically any insult such as fucktard, retard and idiot. It has a myriad of uses and can be used in any shitty sentence you can think of such as these.
"OMG! I heart Fall Out Boy! anyone who doesn't is like a total dickhead! lol!11!1"
How one becomes a dickhead: