If I caught my brother wearing my panties I would laugh my ass off and call him Nancy! I would of told him I was telling everyone what I saw unless he did his make up and a wig. Then I would drop it or he would put my head through a wall. But I never saw my brother wearing my panties so we don't have to worry about that!
my sister knew that I wore hers, so on the days she was on the rag she wore mine, said they were more comfortable with the pad.
Not my sister's panties, but I was using the hotel laundry and found a skimpy thong (mesh with just a little string in the back) in a junky looking basket in the corner. I took the thong into the men's room, wore it, jerked off in it, then took it off and wiped all of my cum off with it.
I threw them back in the basket and sat reading magazines. Almost an hour later, this blonde girl in her mid twenties comes back and picks up the basket. She pulled clothes out of the dryer and put them in the basket with the thong. I'm not sure, but I think she washed the thong before I got there, dried the other clothes and left the thong in the basket to air-dry. I wasn't about to say anything and freak her out (yeah, I know it was freaky).