Before I begin to propose my question to Bullhorn (or anyone who subscribes to the flat-earth theory) I would like to state two facts that I would assume we could all agree upon:
1. Distances can be measured.
2. The shortest distance between two points is a straight line.
Now if anyone can refute these two simple facts, then my argument can be proven false. Otherwise, hear me out.
Bullhorn stated the following in a previous message "I will point to the official seal of the United Nations which lays out the true map of the world
www.un.int."
Here's an illustration of the United Nations map with three points indicating three major cities in the word and their approximate locations on that map:

As you can plainly see, according to this map the distance between points A (Buenos Aires) and C (Sydney) should be more than twice (2x) the distance between points A (Buenos Aires) and B (New York). This would mean that the distance between A and C should be approximately 14,000 miles (according to the rough measurements taken from this map).
However, the actual measured distance between A (Buenos Aires) and C (Sydney) is 7,336 miles; which is nearly half of 14,000 miles it should be if the earth were indeed flat. Clearly, the disparity between the actual measured distances between these cities and their locations on this map do not add up.
Now, for those of you who subscribe to the flat-earth theory:
how can this map, or a flat earth for that matter, be true? I feel that people should have every right to believe what they want, but with such a great difference between actual calculated measurements and the most basic version of the "UN map", I'm just not buying it.
What I am trying to imply is that, using basic logic, a flat earth makes no sense. You would not even have to physically measure any of the distances given. One could just take a plane ride and compare the time it takes to fly from Beunos Aires to New York City to the time it takes to fly from Buenos Aires to Sydney. If the earth were flat, it should take more than twice the time to get from BA to Sydney than it does to go from BA to NY. Also, in order to take the quickest route, you would have to fly over the United States at some point while traveling from BA to Sydney, which just doesn't happen in the real world.