horns and halo effect

noun

a tendency to allow one's judgement of another person, esp in a job interview, to be unduly influenced by an unfavourable (horns) or favourable (halo) first impression based on appearances

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