It's not your "bony butt." It's the SEAT.
THE REAL REASON IT HURTS
Economy seat pitch has shrunk about 3 inches since the '90s, and the "padding" is thin foam over hard plastic. On a long flight, that means your entire body weight gets concentrated onto two coin-sized bones — your sit bones — pressing them into a hard shell for hours. That's what causes the soreness, the numbness, and the "dead" feeling by hour three.