someone who is being a total ass and doesn't quite know it though it is obvious to everyone else.
1) "Mike, you are such a Jerkanoff! I can't beilive you'd make your girlfriend bring barbecue sauce for you to the fair and you don't even thank her for it!"
2) Telling him that he sucked at his solo was such a jerkanoff thing to do! He doesn't have any confidence in himself anyway!