McFlakey
n.,someone who is unreliable, and/or absent-minded, flighty, fickle. Generally irresponsible. 

Friend:  What's up with you and Casey?

Me: You mean McFlakey?  We were supposed to go out the other night, but he never showed.  Told me the next day he went home and decided to go to bed instead.  He's a real McFlakey.