Why do we always lash out on our family members everytime they tell us something?

I have a grandmother that i live with. she buy 6 packs of beer almost everyday. Me and her live in a townhouse two bedrooms and two restrooms. That the reason she got the townhouse so that i can have my own room. Now she acting like i can't be in my room for so peace and quiet sometimes. Just today we had a argument over about eating down stairs. She told me that i going have to start eating down stairs. That when i say why and she said because i so and i told iam 18 years old and i have a table in my room that i eat on. Then i was slamming my room door 2 times and yelling at her from upstairs telling that iam 18 years old and that iam moving out . My grandmother was probably drinking at the time and that why she told me that to eat down stairs just to mess with me. she in a bad mood. that doesn't mean that she can tell me what to do like a little kid. We had an argument like this last year because of me always going up to my room sometimes just because she was saying where you going and what you doing and stuff. All i say is to leave me alone and just let me be i don't bother nobody or not. She just mess with me when she drinks, she an alcoholic. My mother was living with us when we had the argument today. she was scare when she heard me yelling at my grandmother and slamming door 2 times.i was slamming the doors because my grandmother was running her mouth. My unstable mother came into my room and told me to say sorry to my grandmother, but i didn't say sorry right to her face, i just said sorry from upstairs. And i still ate in my room because it's my room and i have a black table in my room that i always eat on and i always clean up and i never make a mess. I pay the whole rent in the townhouse apartment that we live in how the hell can she tell me to not eat in my room. she works when she wants to that if someone call her to go to work.she hardly pay her rent in the last apartment when live in we had to sell things and that why we live in the townhouse now because my social security pays the whole rent. she works for a nursing agency and she works if they call her for works . if nobody call her from work she doesn't get paid and if she does't get paid she can't paid the rent. she sales her own tv to pay the rent if she had to. She need my social security to pay the rent so how she going to kick out . Saying that she don't need me to pay the rent. i call my uncle on my cell phone and told him what had and he told me to hold me anger in and told me to pound my chest when i get angry and told me to just be happy and told me to learn how to hold my anger in because my uncle have bi polar issues. my aunt was trying to call me on my cell phone because she was probably talking to my grandmother on her cell phone so i didn't answer it because i didn't want to speaker to her. Me and my grandmother argue one time this is the second time we had an argument. i just pray that we can just get along sometimes without her saying stuff to me just because she drinking. i understand that she been through a lot just leave me a lone. My uncle wants me to live with him so i don't have to deal with my grandmother mess anymore but i not she though because my uncle have bi polar issues and he a control freak. i really want to live with my grandmother because my college is over their were she live and trans portion on bus is easy over their. I just hope that everything works out. can you give me some advice?