It always bugged me as a kid when you didn't see panties when you obviously should. Not because I was a perverted child but because it just didn't make sense to me. If a girl character was wearing a skirt, naturally certain angles should be drawn where you could see panties. But often skirts would bend weirdly or act incorrectly given the angle or gravity, and it made me irrationally angry because it was wrong.
Now of course it bothers me because I am a pervert.