I am a manager at the store I work at, it is a small business and I have a coworker I do not particularly like. They are someone I have had to set boundaries with twice now because they did not get it the first time. This is someone who likes to antagonize me, pick on me, and has even argued with me before. Yes, my manager knows this, and I had thought this coworker and I had worked things out. 

I had set my boundaries, told them to drop it and it is fine, and that we just need to coexist at work and be fine but adhere to the boundaries. Today when it was nearing the time for shift change I was starting to feel anxious, I knew it was going to possibly be uncomfortable which was fine but I just did not want them to be weird and bring it up again especially since I had previously said to not. He got really close to me when he came in to say hi while I was talking to my coworker and that is when I just could not handle it. I left for a second to do something with another coworker and they told me I need to stop and calm down cause it is fine but my anxiety was so high. 

I was outside with one of the complex cats and they came out and were just staring at me while I did this and then shut the shop door, and asked if things were fine and if we were good and I snapped and said to drop it, and that I already said to stop bringing it up. And the rest of the time I was there before the person came in to switch with me I was just on edge.

Am I overreacting? I have talked to some of my coworkers about this, and I feel like they all think I am overreacting but I am so frustrated that someone disrespected my boundaries which I have worked so hard to be able to put up, and this has been bothering me for weeks, and I have been open and forthcoming about these boundaries with this person. How do I stop feeling uncomfortable? I have to work with them tomorrow night, and I am afraid everyone thinks I am overdoing my frustration but this person only acts like this with me