Explanation: Crumbs are the little pieces of cookie or bread that fall to the table as you eat; the “b” in the word crumb is silent so it sounds like “crum.”
“To feel crummy” means to feel a little bit sick, not too well but not full-on sick. This joke plays on the words crummy and crumb-ie (crumbie is not a word but puts the “ee” sound at the end of the word “crumb”). That’s just a little joke-ie for today. I hope you are feeling well and not crummy.