说俗一点，就是“跟屁虫”……

If you mean paparazzi or someone who harass you.You can say "变态biàntài" to him or her.变态means abnormal. 变态 can used as n. or adj.Example:你这个变态！You are an asshole! 你真变态！You make me sick! （I am passionately opposed to racial discrimination.）

俗语中叫做"尾巴"

高视阔步者(gāo shì kuò bù zhě)

跟踪者，跟踪的人。 I was just with them. Why? - Scott is. We think he could be Dan's stalker. 我刚跟他们在一起，怎么了，-斯科特他。 我们觉得他可能是丹的跟踪者。