A generic term used to describe one who engages in a particular habitual behavior. Fill in the "blank"s with whichever behavior fits the individual in question.
Blanky McBlanksalot sure loves to BLANK.
What a surprise, Crappy McCrapsalot needs to use the bathroom again.
You're just never happy, are you, Whiny McWhinesalot?
Jerky McJerksalot needs some "alone time", if you know what I mean.