I currently have a conflict with a coworker (just call him Bob). Now he is challenging me to a fight. I am actually a violence free men: I think a fist fight is useless. I tried to convince him that it is useless but he thinks that I am just scared to fight him (maybe I am, he is bigger than me after all).
I currently have a girlfriend and I love her (she's not in our workplace). He knows that. Bob and I had no problem with each other at this time.
One day, there is a new girl (just call her Alice) working at my company. She is pretty but I don't have any feeling to her. I still love my girlfriend and will always be, but sometimes I tease Alice just to play around and she know I am just kidding. It seems like Bob didn't think so. He liked Alice and he thought that I want to get her heart and dump my girlfriend after doing so.
I think that it is a very stupid way to think. Because I never think that way. I and Bob talked about this once; I explained that I just like talking and make somebody laugh including Alice. Sometimes I do that by teasing her. After that talk, our (I and Bob) relationship is better. But, after a while, I think he started to hate me again, seems like he thinks that what I said to him before is a lie and that I actually want to get Alice and leave my girlfriend.
Now, he wants to fight me because he thinks that I am a jerk. From my point of view, I just didn't want to have any conflict, if he thinks I am a jerk, than so be it. I don't care losing a friend, but if he wants to fight, I am thinking about my health, I am not a physically strong person. And a fight will make my daily life a mess.
So, how can I talk to him to prevent a fight?
Additional Information if that necessary. I am a 25 years old man and my coworker is around 30. Alice is around 24 (I don't know exactly I never try to remember).