Mupper has come to have a few meanings. It started with a 3 year-old saying it to one of us and all of us say it constantly now. Our aim is to get our entire school saying it by the end of 2002 and to get it in the Collins Dictionary by 2010. A mupper is basically a gom, or an eejit, but it can also mean the coolest person going. Kind of hard to put into words :o) Example: Hey, Ciara, ya mupper! How are you?! OR You are so mupping cool. OR I can't believe you did that! You're such a mupper!
MUPPER
Meaning of MUPPER in English
Slang English vocab. Английский сленговый словарь. 2012