1. Someone who teases by mocking or arousing another person's curiosity and not satisfying the situation: Timmy was a vexer who liked to torment and tease his younger brother and this disturbed their mother very much!
2. A person who harasses someone playfully or maliciously; especially, by ridicule; and so infuriates him or her until some response can be achieved: The teasing and taunting by Sally, the vexer, angered her older brother so much that he went to his bedroom and locked the door so he could watch videos on his computer until he was ready to go to bed.