How to handle a rude colleague who won’t back down?

There is a guy in the office who has been giving me a hard time since he learned that I went out with a co-worker. It first started when he started harassing me about what happened between me and him. I wrote a lengthy response explaining that it was very immature of him to disturb me like that. For two months, things looked ok and he improved his attitude. However, the other day when we went out to have coffee as a group he once again tried to threaten me claiming that I was sitting on someone’s seat. (I clarified this and I was not by the way). It was purely an act to disturb me. I’m thinking of escalating this or talking to him directly since it is not the first time he harassed me. Any advice?

How to handle a rude colleague who won’t back down?
Post Opinion