there's no fat in standard adult weights! (literally)
The standard male weight on my load forms for chartered is 83kg.
I'm fit, run 3 times a week and have a Body Mass index right in the middle of the recomended band - my weight is 75 kg. That leaves 8kg for clothes, shoes, coats and cabin baggage.
Given that I am devinately in the bottom 1/2 of the population Body Mass index wise, and probably somewhere in the bottom 1/4, then I think you will find that the 'average' male on a flight, fully clothed, carrying hand baggage would tip the scales considerably over the 83kg allowance.
I have actually been weighed as a Pax once -on a flight from Orkneys to Aberdeen!