Is a metephortic "cookie" which one "eats" in order to become more fun, easy-going and less stick-in-the-muddish.
When an uptight, wet-blanket is being difficult and others are becoming annoyed by their crappy antics they need to eat a Flexie-Cookie to get back to being awesome.
An imaginative cookie that helps you poop out that giant stick up your ass.
Stick-in-the-mud: No, I'm sitting in the car, that sounds annoying.
Fun Girl: Somebody needs to eat a flexi-cookie!
Fun Girl: We're going about 10 minutes late.
Katie P.: Uuuuugh. Come on I could have organized my monthly receipts in that time.
Fun Girl: Katie, do you need to eat a Flexie-Cookie?