I'm not sure what your situation is exactly. Its best to nip it in the bud early on by either talking it out with the person, setting boundaries, or if they're the type who just wants to harass you, start documenting it or report it. If you are too quiet, isolated, or un-confrontational, there are people who will take advantage of that.

There was a man I barely knew who was harassing me for a while and my response was to ignore him, and I wish that I had actually reported it or told him to F off, it would have made me feel much better and safer. He was using me as an emotional punching bag because I hurt his precious man fee-fees by not being friendly and interested enough. I ignored him because I don't trust or care for men who act that way, my ignoring him was fueling his anger, my lack of response-and consequences- made it appear safe for him to continue bullying me, and he didn't have the emotional maturity to let it go and move on.

Sometimes you need to directly tell them to piss off, or they might see your ignoring them as a sign of weakness and they'll consider it safe to continue. Let them know that there will be consequences, and if need be, start documenting and reporting harassment.