Someone who acts like a nigger/ black person. and who happens to be white.
black person: yo dawg, whats good?
white person: nigger i be mad chill right now imma go to da club nd hit up 'em pussy ass bitchez
black person: wow you think your black imma beat your ass with a stick nigratomous.
In this situation the white person is the nigratomous and the black person is actually a nigger.