When a healthy person blessed with good metabolism condescendingly explains things to someone less privileged than themselves. They've most likely never struggled with abnormal blood pressure, eating disorders, their body image, allergies, or any other disorders which would interfere with their ability to keep fit. Fitsplainers particularly enjoy wasting time lifting weights, training for marathons and spending exorbitant amounts of money on food and supplements.
"Losing weight is easy. Just get a good night's sleep, get up early, and train and exercise in the morning. You don't have to spend all your time on your kids."

Person 1: "You need to spend the extra money on organic food if you want to overcome your irritable bowel syndrome."
Person 2 "Way to fitsplain something you know nothing about, you ignoramus."
by Bloopy November 13, 2017
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