inverted snob

noun

a person who scorns the conventions or attitudes of his own class or social group by attempting to identify with people of a supposedly lower class

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012