The origin of pillock is believed to go back to the 16th century meaning penis from the Norwegian word pillicock, presumably akin to the slang dickhead meaning inept fool.
pillock (plural pillocks)
- (Britain, mildly pejorative, slang) a stupid or annoying person; simpleton; fool.
- ^ http://www.allwords.com/word-pillock.html
- ^ http://www.answers.com/topic/dickhead