All cards are blank inside but here are some suggestions to help you get started:
Just write a bunch more 'Yay's maybe. Just like way too many, make it seem like you are unstable.
"I knew you do the thing you did"

This card is printed on handmade paper and printed by hand, so naturally, it all has variations in color, texture, and print. Perfectly imperfect just like you like to tell yourself you are.