The word “teasing” can have multiple meanings. When teasing is done in jest, or to be playful, it is relatively harmless; however, when teasing is persistent or unwelcome, it can be regarded as harassment or bullying. A common form of teasing is verbal bullying or taunting.
When the intent behind it is hurtful, it is seen as bullying, especially if it involves some humiliation and social rejection. It all depends upon the way the teasing makes the other person feel. A difference in power is what makes teasing go from being playful to harmful.