The guy who's average day involves no movement, and then a cheeseburger and milkshake for lunch before talking with his bros as the gym and then coming home for

The guy who's average day involves no movement, and then a cheeseburger and milkshake for lunch before talking with his bros as the gym and then coming home for a few cold brewskis is convinced he's got one of those "big" builds you're talking about and that standard BMI doesn't apply to him. He's only imaginary, but I'm pretty sure he's wrong. The assessment you're trying to make just isn't reliable.