To cut down on something means to reduce the amount of it:
I’m trying to cut down on coffee.We need to cut down on unnecessary meetings.She’s trying to cut down on screen time.
So why is the joke funny?
The expression cut down on excuses means make fewer excuses. But the speaker deliberately interprets cut down literally and decides to make the excuses shorter instead.
Owe up to - Phrasal Verbs - ACR Idiomas 🤔 "I wanted to own up to eating the last cookie... but someone else got away with it first." It sounds like a joke—and it is. But it's also a great example of how native speakers really use English. Many learners try to memorize long lists of phrasal verbs. The problem? Most of them are forgotten a few days later. A better approach is to learn them through stories, conversations, and humor. In this joke, you naturally learn two useful