“Oh shit. It totally slipped my mind.”
You made plans with your close friend to meet up at a park to go jogging together. You forgot about it until your friend called to angrily ask where you were. You say this in response.
Oh shit. It totally slipped my mind.
This is something that people say when they realize that there's a problem and are suddenly worried.
"Shit" is a curse word, so there are a lot of situations in which it isn't polite to say it:
- around strangers
- to people who you are trying to impress, like your boyfriend or girlfriend's family
- in church
- if you're a child
There are some people who don't say words like "shit" at all. But most people do use curse words with their close friends and sometimes coworkers.
When you say that something "slipped your mind", it means that you forgot about it. People use "slip (one's) mind" for talking about forgetting to do tasks, or forgetting people's names.
If you didn't remember something at all, you can say that it "totally" or "completely" slipped your mind:
Oh my God. I was supposed to send that off by the 22nd, right? It completely slipped my mind.