Ladies, why does my sister dress so skimpy around me?

I don't have a brother, so the problem never was presented with me. But it sounds like she is more comfortable around home. I dress skimpy around my house because it's more comfortable than four or five layers. (plus it's super hot where I live) So maybe it's her feeling more comfortable around home. But from what you say, it does sound like she is teasing you a little. She probably feels confident seeing you glance at her. So she probably isn't mad about it or else she would cover up. If she makes a big deal about it, tell her that she shoudl cover up.