There are several collections of aircraft design horror stories, like Gilbert's "The World's Worst Aircraft". The collection usually includes Henri Mignet's "Flying Flea" and other classics.
My own collection adds some less obvious cases, highlighting more subtle design flaws. For the most part, these are cautionary tales. Don't do what they did. The possible exception is Molt Taylor's "Bullet".
Click on the tab "case studies" if you want to know more.