Funny Sayings What Is It Called When You Use Funny Sayings Or Quotes In A Letter ?

What is it called when you use funny sayings or quotes in a letter ? - funny sayings

I answer a questionnaire about certain things, and I'm on a lot of sentences like: "Adding Insult to Injury", "For gasoline on the fire," etc., etc. Finally, I want to explain to their use often, but what Did you call? I want it but sound good! And I want to use the text or quotes or something.