Given the name from Peter Kay's "Uncle Knobhead"
similar to being two faced
2) Nagging someones head to make them tell you if they like you or not, and when they finally answer you, you shag their friends.
3) Telling your friend your going to the shop to get something, whilst really your goin meeting his/her ex-boy/girlfriend
4) Makin a brew at your mates house n not makin them one.