Yeah, this IS the right way round.
I have a sister (19) and no-one else other than our parents in the house. Unfortunately, our house is like Heathrow over the holidays. Mum and dad have house guests pretty much every night.
I was lying on my bed staying out of the way when, with not so much a knock, my door flew open and my sister was standing there in a long t shirt with her duvet and a pillow.
'Move over and shut up!' (Charming)
It turned out our parents had invited people to stay over and Charlotte had been told to give up her room. She threw her duvet over me and then scuttled under it.
It is far from the first time we have shared a bed, but Charlotte was wearing, well, not very much. As she tossed and turned, I got a good look down the top of her t shirt. (No bra, her small but perky tits looked quite nice!)
Every time I moved, Charlotte said 'Oh for F.... sake will you stay still.' Well, I put up with her behaviour for about an hour before I had finally had enough. 'Now, you listen here, you bad tempered cunt, you are in MY room now, and you will mind how you talk to me? Got it, you f....ing bitch!'
All I got in return was tight-voiced 'Again. Call me those things again.' So I just laid into her. 'You evil tempered f....ing slut. You f...ing CUNT.' Then Charlotte just started twitching and gasping. 'ohh ohhh fuckk fuuuuuuuuuuuuuuuuck.' And I knew in that moment that she had been playing with herself right next to me.
I don't know but that got me madder than anything. She barges into my room, gives me a hard time THEN gets herself off!
I was about to punch her when I felt her take my hand and shove it into her wet knickers. At the same time, she grabbed my cock and started to wank me.
It went WAY beyond that, of course, I can't give details here.
The following morning, we woke up naked and I masturbated her to another orgasm and she returned the favour to me.
Where this leaves us I don't know. It is certainly the first time we did anything sexual, but I have a sneaky feeling it won't be the last.