Why do guys get mad when girls reject them?

There was this guy whom I was best friends with for 5 years. We met online but the way our connection was, you would've thought we were friends all of our lives.

Yesterday, out of no where, he expressed to me how much he liked me. He was calling me "his queen" and things like that which made me very uncomfortable but I just allowed him to voice his feelings. I then told him that by me coming out of such a traumatizing relationship, (which he knew about as well) I wasn't interested in dating anyone right now and that I would like to fully heal and focus on being a mom and bettering myself.

However he was still persistent and proceeded to ask me to give him a chance over and over for 10 minutes, in which I had to keep saying no. He even tried to guilt trip me by using the "I'm a good guy" line.

He hung up on me, which let me know that he didn't take that well. At that moment, I was mentally done with the friendship.

So today, he tried calling me and I tried nicely telling him not to call. He asked why and I told him that he made me feel uncomfortable with the conversation and the way he reacted. He then started cursing me out and going on a rampage.
Despite telling him not to call or text me several times, he disregarded that completely and began to bash my mothering and my son.
Why do guys get mad when girls reject them?
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