If I may, I'll put the video into my own words -- which may differ from the original. But here is the essence of the argument:
To a fairly high degree of accuracy (for the sake of argument let's say only within +/- ONE THOUSAND kilometers), the distance from North Pole to Equator is known to be 10,002 km and the equatorial radius is 40,075 km. Does any Flat Earther have any other values they can substantiate as being the ACTUAL values, again +/- 1000 km -- (HUGE margin of error, should be easy)?
By trivial geometry we know that a circle with a radius of 10,002 km would have a circumference in the range of 62,844.4 km -- That is IMPOSSIBLY too Large for Earth. Even if
you think that π is 3 that STILL makes it 60,012 km around. You CANNOT make this fit.
Conversely, a circle with a circumference of 40,075 km would have a radius of just 6,378.13 km -- IMPOSSIBLY too Small for Earth.
Therefore the Earth simply cannot be flat if these measurements are anywhere even CLOSE to the actual values.
Of course, I don't expect any Flat Earther to accept simple geometry - it's not in their nature to allow facts to get in the way of a good conspiracy theory. NASA IS LYING ABOUT THE DISTANCES! NASA IS PROJECTING A CHEMTRAIL HOLOGRAM INTO YOUR BRAIN. Ok fine -- believe whatever you what but know this -- the rest of us are pointing and laughing. Of course, that just PROVES you are right - right?
This is actually a very simple and elegant demonstration, well done OP!