I had this dream last night where there was some sort of party at my parents' house, and my brother, who is married in real life and was in my dream, was flirting heavily with a stranger. I had to keep reminding him he was married, which he did not appreciate.
In bed this morning, I thought about what an interesting story it'd make if a married man somehow starts hitting on another woman in front of his sister, and the struggle the sister would have in figuring out what to do and how to do it and what her place in the situation is. Especially if the siblings were as different as my brother and I are.
I think I'll tackle that idea for my second story submission.