I (21M) have been living with my sister who's 26 since the first of this month. I moved in with her because I couldn't find work, and so my uncle was gonna kick me out. A few minutes ago I was playing a video game, and my sister asked me for a smoke, but I didn't immediately get up to grab her one. She's been trying to quit, so I hid her pack and only planned on giving her two today, but she got stressed and wanted a third. I wasn't going to give it to her, but she kept asking me so I decided I was going to give her one after my game. Problem is she kept pestering me, and kept getting ruder about it and said "You don't smoke, you don't understand what it's like to need a smoke, so give me a fucking smoke!" While lording over me. So I just snapped, walked over to the hiding spot, grabbed the whole pack, then threw it onto her bed and told her to stop being a bitch to me.

She then proceeds to walk outta her room, and basically said that she decided to help me out by bringing me here, and said something like "You know who calls me a bitch? Mom, or Shane, they call me a bitch, or Cat". I kinda paraphrased that but you get the idea. She then went onto the deck to smoke while I thought about what just happened. After she finished, and got done using the bathroom a few minutes later, I walked up and said we should talk about what just happened like adults, instead of snapping at each other. She just closed the door in my face, and said she has a final for school to start soon.

On the surface it seems like I'm a massive prick, who couldn't stand up for two seconds to bring his sister a smoke. Reason why I'm posting this here, is for a few reasons. One being she always is so fucking mean to me, and even now that we're both adults and she's supposedly gotten her anger under control, she continues to treat me like I'm a fucking idiot. Second being she brought up her gracious gift of bringing me here, and acted like I'm just being a bum on her couch, when I'm paying for my half of food, cosigning on her loans and car payments, offering to give her the car I was gonna buy because hers is breaking down, offering to give her money to support her when I start work in a few days, doing her damn dishes because she hates doing them, and even left the fucking house for a day once, just so she could focus on school work. Third reason is I'm pissed that she compared me to our parents, as if I'm so horrible to her, when again she just belittles me and is in a horrible mood 24/7, so tye audacity to make me sound like a monster urks me.

We do a lot for each other financially, and she even helps me with my important paperwork, but I'm just so pissed off at the whole situation, and how she wants to act like I abused her and she's this poor victim in all this.

TLDR: I snapped and called my sister a bitch, and don't know if I'm a dick or if she is, or maybe we both are.

Edit: I want to emphasize that I'm doing what I can to avoid being a financial burden, and even giving her more then what is needed to help her succeed in what she plans on doing. I don't really agree with people saying I'm in the wrong simply because it's her house, I learned the hard way that that's a stupid ass way of viewing things, especially when it's family you're living with. She also is trying hard to quit smoking, so people saying I have no right to be in between her and smokes, when its what we both want, is also dumb to me. I plan on talking to her tomorrow when things have cooled off, I'm gonna talk to her about respect going both ways, and that we both can't be shitty to each other while we temporarily live together