I love my sunnies. I wear glasses, so mine are prescription. I had to save up to get them, but its been worth it.
If anyone says anything about you wearing sunnies inside or looks at you funny, you could shrug and say they're prescription. You forgot your other frames and you need them to see. Or if you're feeling brave use the excuse I do. If rockstars and celebrities can why can't I? Bono, Usher, Gene Simmons, Gwen Stefani, JLo, Rihanna, Emma Watson, Lady Gaga and Britney Spears all do.
You can also say you've got a headache, or bright lights hurt your eyes.
Things related to fashion I find tend to be accepted more if you try to carry them it off with confidence. Which can be hard for us, I know.