flat as a tack
(as) flat as a tack
Demoralized or unenergetic. She's been flat as a tack ever since she heard that she didn't get into her top choice school.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
flat as a tackin very low spirits or lacking in energy. informal
The idea underlying the expression is of a tack that has been hammered in so that none of it protrudes.
Farlex Partner Idioms Dictionary © Farlex 2017