How do you guys explain the Horizon? Meaning that the surface that one is observing from is not an infinite plane. On the clearest of days, the only restriction to one's range of sight is the horizon. There can be two explanations for this - one, that the Earth at some point just stops, as if you were looking off the edge of a table (by the way, that means that when something disappears off the Horizon, it kinda just falls off into space, lol). The other is that the Earth is round.
The distance to the horizon is limited by atmospheric density. The atmosphere is not perfectly transparent. That line you see is simply the furthest our eyes are able to pierce through the atmosphere.
Even as a 100% RE'er this is true. Anyone can see that mountains in the distance are obscured by the atmosphere. Varies wildly on the weather though.
Further proof of the Earth being round came after the voyage of Columbus.
Columbus's voyages did nothing to prove the shape of the earth. Why did you bring him up? 
Um. They actually completely proved the Earth is round. He sailed west (obviously avoiding continents) and still ended up at India. He did this because he fully believed in the round Earth theory and look what happened.
When Newton discovered and measured the force of gravity, that number could then be tested anywhere the theory was known. Since the force of gravity is roughly the same everywhere on the globe, it could be surmised that the Earth must be spherical.
Or the earth is accelerating upwards at a rate of 1g.
And is now travelling millions the times of the speed of light ey?
If the Earth were not round, whole hemispheres would have different atmospheric pressure and significantly different sea levels.
Explain this. It sounds like a load of nonsense.
Unfortunately, I can't really figure this one out too.
Also, pictures taken of the Earth in the last 50 years have proved absolutely conclusively that the Earth is round.
Since the earth is flat, these pictures must be fake.
This is kind of thing that good ol' AaronP/sideboob has been talking about. Even if the Earth could be flat, nothing has been proven by anyone. You claim we can't prove the Earth is round, yet none of you can prove the Earth is flat. Since apparently neither of us can prove anything to do with Earth's shape, your argument that the pictures must be fake cause the Earth
is flat is entirely invalid.
Ok, so im thinking you're still not convinced. So, how exactly do you explain all the photos of the earth, taken from space? I guess someone photoshopped them all, good old Nasa, back in the 60's firing up their copy of Adobe Photoshop "this will convince them, what we'll do, is just use the circle tool and pretend the earth is round, ha.. success!".
Photoshop obviously didn't exist in the 60s. Thankfully the pictures produced at that time were quite grainy. It would have been simple to manipulate the images without the use of a complex graphics program.
Lol. The whole argument about the photos being faked for 50 years is just plain lunacy. Are they just going to keep doing this for the next 1000 years?
Seriously... video... pictures.. the fact that people have visited space and have seen the round earth.
Of course, we feel that this is all part of the conspiracy.
Cause the whole world is under some spell by some space agency? What a mind fuck this theory is...
You can also observe, with binoculars, ships slowly 'sinking' below the horizon as it sails farther and farther out to the ocean, then watch them come back.
This was, of course, covered above.
You can also sail or fly around the world.
You certainly can. The FE is laid out like the emblem on the United Nations seal. The north pole is in the center and the ice wall (which you incorrectly identify as the continent of Antarctica) lies on the outside. Traveling east or west you are actually traveling along the arc of a wide circle that goes around the north pole.
Guys honestly, how on earth (excuse the pun) would something orbit a flat plain?
Nothing can orbit a flat plane.
So basically you go straight but in reality physics is just nudging you in an arc to make you think you're going straight? Another mindfuck.
You realise the tides wouldnt work they way they do now, actually.. you realise gravity wouldnt quite work.. right?
Why is that?
Err. The Earth wouldn't have tides. Its like putting some water in bowl accelerating it straight up and then trying to explain why theres no tides...
Heres another one for you... when we have a lunar eclipse, the earth casts a shadow on the moon. The shadow is, go on... i'll let you answer this one... oh go on, please... its... ROUND.
Yes, since ancient times it's been assumed without evidence that the shadow on the moon during a lunar eclipse is that of the earth (which, by the way, is round, just not spherical). Our theory is that the eclipse is actually caused by what we call the Shadow Object, which is close to the sun and therefore not visible in the night sky. It's this object that casts a round shadow on the moon during a lunar eclipse.
Hope this answers your questions! 
So basically you're just making up the existence of another stupid 'object' which explains the phenomenon? Shadow Object? What the fuck? So God's like, "Hey I need to convince these people its a round Earth when its actually a flat Earth... hmmm.. I know! Let's put a black disk in front of the Moon everynow and then!"
Like... What the fuck?
You do realise what a mindfuck
attempting to believe in the Flat Earth theory is right?
Oh and:
Recent scholarship[3] has argued that "with extraordinary [sic] few exceptions no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat" and that the prevailing view was of a spherical earth.