be all fur coat and no knickers

be all fur coat and no knickers

To be attractive on the surface but lack substance underneath. I thought David and I would really get along well, but we had nothing to talk about at dinner—he's all fur coat and no knickers. Our new boss sounded like she had a lot of good ideas for the department, but it turns out she's all fur coat and no knickers.
See also: all, and, coat, fur, knickers