Sunglasses - is it rude to wear them indoors?

[Lolli]

I don't think it's rude, but I will confess it bugs me if I'm talking to someone and can't see their eyes.

[Tinks]

I don't think it's rude to wear them inside but when I see people with htem on inside I do wonder why they're hiding their eyes.

[suse]

I wonder why it's considered rude to talk to someone inside with sunnies on, but not outside? The effect is the same whether one is inside or outside - ie: the eyes can't be seen. I mean, it's obviously because it's not considered necessary to wear them inside, but if one would not find it difficult to have a long conversation outside with someone wearing sunglasses, then why would it be so if they were worn inside?