Anxiety/self-doubt
Greeting card idea:
"Hi, I hope you aren't mad at me. You probably aren't and don't have any reason to be, but I'm constantly paranoid about it anyway. But if you are mad after all, then I'll totally understand if you never speak to me again. But if you do still want to speak to me, I'll be over here hiding from you filled with a mixture of anxiety and sadness. Okay, bye!"