I learned the term “you can’t unbake a cake” from D. Rumsfeld. I use it on my kids!
Least favorite phrase: a “granular view”, meaning to look at something closely.
In my work, I deal with late loan payments. When a customer asks me how to remove a 30 day delinquency from their credit reports, I tell them that you can’t unring the bell. What’s done is done. They were late and it’s been reported.
If they persist in getting it removed, I have also been known to tell them to invent a way-back machine. Then go back in time - pay the payment before the 30 days - and “problem solved”.