Bonus points if the author first mentions a specific trait, physical build, or whatever else halfway through the novel and totally fucks up my mental image.
I don’t expect a biology model description for each character, but write me something brief and evocative of how they should look, you fucking dork author. I don’t even know how tall she should be, her hair colour, anything. Why are you like this, author?
Usually I’m not interested in what made-up people make-believe look like unless it somehow drives the plot or develops the characters’ relationships.