Because it's her home & she should feel free to be naked or in her undies?
You should realize it's natural to get excited over the female body but remember this is your sister's body.
hi at first how old are you and she ?
i hate to pop your incestual bubble but she is most likely just being comfortable in her house and around her dear brother who she would never suspect is having weird thoughts about her. just leave her alone or start walking around in your underwear if she says anything tell her you will only cover up if she does. if she refuses then you can both be half naked all you want.
I think it's pretty weird that she does it when its you and her alone. I mean it "could be" that she is comfortable walking around almost naked in the house but she knows she can get in trouble by your parents. But then...why a thong? it could also mean she is trying to seduce you. I think you should tell her you are uncomfortable with her wearing that and she should change into more appropriate attire.
I would say " listen asswipe put some damn clothes on...I am your brother! Hello?" She is just strutting around trying to show herself off to you basically...for her own little thrill
Personally, I wouldn't walk around practically naked in my lingerie.. I mean, it's a little odd. Is she older than you?
I mean, it's almost natural for a man to be aroused by women in skimpy attire, but for your sister? I mean, as long as you don't have feelings for her...
ew...why would you let yourself get hard...gross. =( She's your sister, tell her to put some freakin clothes on for pete's sake. Tell her it's gross.
Well one way to possibly fix it would be to invite a few guy friends over every now and then unexpectedly =) If she's remotely shy, it'll end soon enough.
You're lucky. Maybe she's implying she wants you if she's doing this regularly.
It's somewhat natural to feel excited when you see boobs and ass, especially if your sister is in her prime. Just tell her that you don't feel comfortable seeing her in her bra and thong. Otherwise, just don't pay attention to her at all.
Tell her to put some clothes on before you call the cops on her