Why do guys like sniffing my panties?

I live at home with my parents and my older brother, I'm 19 and he's 25. Often his friends are over and many times after they have left and I go up to my room I find the hamper in the upstairs bathroom has been gone through, (my brother and I live on the second floor and share a bathroom), and very often pairs of my worn, dirty, panties that I know I threw in there are missing, gone. When my brothers friends are over here they hang out upstairs in his room and use both of ours bathroom and hampers. A friend of mine told me that it gets them horny smelly and sniffing and also licking them too. I'm not really sure why it's so exciting for them to do? It also bothers me because who ever he is, he has good taste cause he's taking my favorite ones. lol This has happened maybe 3 times already, and one time 2 of my bras went missing too. Has this happened to anyone else?