Thin privilege is walking down the street and having cute women check you out. Honestly if any fatties are reading this, I can tell you there is no greater motivation or better feeling to get yourself in shape and take care of yourself than being out in public and getting consistent attention from attractive people of the opposite (or same if thats your thing) sex. Even though it's kind of a silly and superficial thing you cannot overstate how great it can make you feel. I've tried plenty of drugs and it's a stronger rush than any of those.