When applied to girls: the quality of being unaware of - or otherwise unaffected by - blatant perving.
Gavin: (staring at Karen's breasts) Wow you have beautiful eyes.
Karen: Aw, you're so sweet.
Onlooker: Karen is totally impervious.
not permitting penetration or passage; impenetrable, incapable of being injured or impaired:
The coat is impervious to rain, wear, and tear.