On NPR the other day a float maker was describing his entrant to the Chinese New Year parade. "I just hope it's not a barn queen," he noted.
A 'barn queen' is a float which looks great in theory and is really beautiful when it's being designed but once you get it out into the parade it just doesn't live up to expectations. Either it doesn't wow the crowd as hoped or some aspect can't stand up to the rigors of actual use.
Hands down this is my favorite new expression. Can't wait to apply it to projects and people.