Uncivilized Monsters Of Poverty. Its commonly used in a derogatory fashion by "well to do" snobbish rich kids to describe those of a lower class.
"look Charles. It's those damn u.m.o.p.'s sitting on that green box again. lets go this way instead, I wouldn't want to get AIDS if one were the breathe on me. well said. indeed."
by David Cummings December 08, 2006