I think 不要欺负某人 means "Don't bully someone". I'm pretty sure 欺负means to bully someone, in English, "bully" can be used as a noun too. Not sure whether or not it's used that way in Chinese, but here are some examples of how they look in both as verbs and as nouns:
In this sentence it's used as a verb:
Sarah! Don't bully that helpless nerd.
In this sentence it's used as a noun:
Sarah's just a big bully.
Hope this helped.