Noun
cheat day (plural cheat days)
A day on which a person on a diet or similar restriction on activities is free to disregard them.
I give myself a cheat day where I annihilate my diet. I'm an all-American girl, so I go for a burger and fries and a shake. Ashley Wagner
I have days when I say, 'I'm going to have five chocolate chip cookies today.' I'll have a salad every day but every week I have a cheat day. Melissa Etheridge