"em raef" is simply "fear me" spelled backwards. It is a hidden message used to alert people that they should not feel safe around the person saying it.
A little boy was playing soccer with his friends, suddenly one of them kicked the ball over the fence to neighbour. The little boy went into the yard, his friends didn't see him again.
Then one old man came out, and shouted "EM RAEF!", the boys got really scared and ran away.