If you think this sounds crazy you’re not alone. Let me explain.
Yesterday my brother’s girlfriend had a promotion and they invited us to have dinner and celebrate. When we (bf and I) arrived at the restaurant my brother and his girlfriend were there, sitting in chairs waiting to be seated inside. There was no other chair and I was wearing heels and was a little uncomfortable so my brother offered me his chair but I just told him not to be silly and sat on his lap for maybe 2-3 minutes until our table was ready. That was it.
When we got home my boyfriend basically “confronted” me about what I did and said it was a stupid thing to do. He explained that things like this might cause my brother to develop a sexual interest towards me and it’s not good. I think it’s nonsense of course. He actually said that he could feel my brother getting hard or something (how? I have no idea). He says that in general I should act less slutty with my brother. I asked him to make some examples of my slutty behavior but he said general things (no specifics). I wasn’t in the mood to argue so I just said whatever. This morning he talked about this again and I get the feeling he’s not gonna let this drop. I literally have no idea where this is coming from.
tl;dr: Boyfriend says I act slutty around my brother and this will cause him to be sexually attracted to me.