Is he interested in me or is he a jerk?

There is a guy at my job who had a gf at the time he was hired. We did do some
flirting.He later started to bother things at my desk or anything he could do to annoy me, and looking at me like he was lost in my eyes. His behavior was kind of cute at the time because I figured he liked me. I found out he
broke up with his gf later this year. He then started talking to me in away that made me feel like he was trying to insult me or make me feel dumb. He became even more annoying. A coworker had picked up on our flirting previously and called he out about if he like me. He danced around the question. I started to ignore him and he would still stare and me. He then upgraded to trying to start arguments with me and would try to have the last word after every comeback he threw at me. His behavior was irritating but I almost contemplated reporting him to HR. He almost made
me almost curse him out so I did nothing but gave him a look that could kill. All he did was smile back. Recently he said to me Well someone have a new hair do. So I joked back to him saying he must wants the same hairstyle since
he's asking so many questions. This time I got him to shut up and I just smiled at him. I know I should be more assertive,put him on the spot, and ask him what his problem is since this behavior has been going on for about 8
months. I know he is going to just deny or say something to get me riled up. What should I do?