1) Someone who constantly and compulsively uses things that arent generally considered to be "mainstream", or the alternatives to mainstream things, for the sake of being different.
2) Someone who changes standard, generally-accepted colloquialisms into less known versions (i.e. 'Bing it', rather than 'Google it')
Person A: "I'm going to Yahoo Search that..."
Person B: "You utter alternativist.."