I have not had any bad experiences looking in mirrors in dreams, though these are non-lucid dreams, as I'm just starting to learn lucid dreaming. In one such dream, my reflection in the mirror looked really great (though not much like the actual me, and not wearing clothes I would ever wear), and in the next, I looked just like myself, but with longer hair. (In the dream, I thought, "That's odd--wasn't my hair quite short just earlier today?" but didn't realize I was dreaming.)