[take] the gilt off the gingerbread

to cause something to be less enjoyable as it could be

The idiom "take the gilt off the gingerbread" comes from the idea of removing the attractive, shiny, and decorative layer of gilt (a type of gold leaf) from gingerbread, making it less appealing. Figuratively, it is used to describe a situation where something has lost its initial charm or allure, making it less attractive or enjoyable.

We had a great trip, but our flight home was badly delayed, which took the gilt off the gingerbread.
The unexpected repair costs took the gilt off the gingerbread of their new home purchase.
The excessive work hours and stress took the gilt off the gingerbread of the high-paying job.
The negative feedback from critics took the gilt off the gingerbread of the director's highly anticipated film.
The constant arguing and conflicts have taken the gilt off the gingerbread of their once-happy relationship.