cheat day

[ cheet dey ]
/ ˈtʃit ˌdeɪ /

noun

a day in which a person goes off a dietary regimen: Today’s my cheat day, so I’m eating pizza and ice cream.

Origin of cheat day

First recorded in 1980–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019