I'm a 21 year old college student living with my girlfriend, her mother, and her mother's boyfriend. We've lived here, on and off, between my house and hers for the past 5 years. I don't consider this to be my house, but her room, at the very least is my only private space in the house.
Recently, (around a year ago) her sister's ex-husband and their son moved into the house. It's an incredibly weird situation, but my grandmother likes having the time around her grandson. I've never really had an issue with him in the past, as he's relatively young, but he is a bit of a brat and likes to get things his way.
As of late, she's been spending more time out of the house, and so there are periods of time where I'm alone in her room, and for whatever reason, her nephew (the aforementioned grandson) likes to come in. I try to keep him out, but there's no door (the room is the attic), and he has a habit of helping himself to my things. I don't really have a problem with that, but he's not very considerate with them, and his favorite word right now (he's 6) is no. Particularly when you tell him not to do something.
I have a good temper. I don't yell at people, and my preferred method of conflict resolution is talking it out. But he's not a particularly talkative six year old, and as anyone with a young child probably knows, he's not one to be reasoned with. He's very fond of punching people and doing what he wants, despite our best efforts, so he's not always an easy kid to deal with. For the most part, he respects my boundaries if I'm firm with them.
Today, however, I told him, "I'm very busy with homework and I need you to go downstairs." He was playing with a little writing tablet I use for doing math, drawing on it a little violently, but I figure he's a kid so I let him do it. When I asked him, he said "No." I said "$Name, please go downstairs." "No.", this time more insistently, "$Name, go downstairs now." "No."
At this point I was very frustrated with him, so I looked him in the eyes like I was very serious and firmly said, "Go. downstairs." And he stuck his tongue out at me, threw my writing pad on the ground and said, "NO." So I grabbed the back of his shirt, got down on his level and said, "Now." And he got a scared look in his eye and ran downstairs.
I don't want to have to do that. To be honest, it made me feel a little sick treating a kid like that, but I didn't know what else to do. His grandmother, his father, and my girlfriend don't take anything he does seriously. If I asked my girlfriend to make him go downstairs so I can work, she'll do it, and he mostly listens to her, but everyone else just laughs it off.
Normally in this kind of situation, I'd go to speaking with an authority figure in his life, but his father is never home to discipline him, and his grandmother is the kind of person who solves interpersonal conflicts with screaming and anger.
Obviously the answer in the long-term is to get a better living situation, but until I finish college and get a full-time job, that's not exactly on the table. I just want to know what I can do in the future to try and alleviate that kind of situation without having to be mean about it. Another concern is, today I was afraid I'd be in trouble with his grandmother for speaking to him in that manner -- luckily nothing came of it -- but he has a habit of crying wolf and I don't want anyone thinking I'm physically abusing him. I really really would prefer not to have to do anything of the sort, I just want to be able to get alone time when I want it.
Thanks for making it through the wall of text if you've made it this far. Open to any comments, criticism, or advice.