I've posted about this before as a poll as they've been seemingly ready to fight for ages, and they finally did just recently. This is the first time they've had a realistic opportunity to fight and they did.
So my parents were on holiday and me and my GF went to pick something up from their house, we entered, and as expected my sister was there and as soon as I collected what I was going there for, my sister just looks at us and says "you can leave now" my GF just looked at her and sxxxxxxxed and my sister just walks over to her and punches her, it wasn't a great punch but it caught her by surprise. After that they both grab each others hair and start swinging at each other, and it looked like my sister was landing good punches at first and I was getting a bit worried, but suddenly my GF swings my sister to the floor by her hair and gets on top, she lands a few punches and my sister screams out saying get off and she's done. My GF stops punching and after a few seconds gets up, so disappointing for me, but then my sister gets up, takes a breath and attacks my GF again, my GF was facing her though so it didn't really catch her off guard. They stood up a lot longer this time pulling hair but again my GF managed to take my sister down into the same position and this time she was angry. My sister covered her face as my GF was throwing punches down at her and pulling her hair, and again my sister screams out she's done but this time my GF replies "I'll stop when I want bitch" And for the next few minutes my GF was sat on top of her taunting her and pulling her hair. My sister couldn't get up until my GF finally got off her, but my sister stayed laying on the floor covering her face as me and my GF left.
Sorry this isn't a long story, but hopefully people can enjoy it anyway.