Is it normal to always wanting to have the last word?

I am considered the blacksheep of the family mainly because of my mouth. I tend to say what's on my mind whether it hurts peoples feelings or not. I am very hot headed! And Impulsive! After I calm down I feel really bad for what I did or said but appolozies only go so far. My mom always tells me I act trashy and that hurts but it's like vomit I can't help it all I think about when I'm mad or hurt is to hurt them back so they feel like I feel. It's really hurting my marriage and only a couple people in my family even talk to me. My brother is due to have his first child in August and because I cussed his girlfriend out thinking I was helping my brother out because she was mistreating him. They said I'm not welcome to be there when the baby is born. I really am a good person as long as people don't rub me the wrong way.