I Caught My Brother's Friend Sniffing My Pánties; Please What Should I Do?

My Friends Brother who is btw 17 or 18 came for a Sleepover, am 25 . My Parents were out and wanted me to pretty much 'babysit' them while they were away. 

 time went by and I wanted to go for a Walk. As I got back went back to my Room I saw with my own eyes my Brothers Friend smelling my Underwear from my Laundry Basket I was so shoked I stubbornly cleared my throat and he turned away swiftly and looked at me, and couldnt say a word,dropped my pánties and left with shame....
later that day I sneakily went into my Brothers Friends bag to see if he took anything, As I opened his bag I saw my Brá and 2 of my Underwear, I just got so Furious but couldn't do much. What should I do about my brothers friend and is it normal? To me sniffing pánties is just disgusting, You are smelling something that someone rubs their Cores on.