MKU
Noun: Mobile Keg Unit

Used at parties a person takes a keg and puts it in a military style backpack, or one that is big enough to fit a keg, they walk around filling up any beers that are  
empty.

The people made into MKU's are normally made to do so as punishment in a bet or in many cases pledges have to as punishment.
Guy 1 "That pledge really sucks."
Guy 2 "Ya well that's why he is an MKU tonight."

Guy 1 "Hey pledge come fill my beer."