Most people don't require the proof anymore, but the clown Rapper B.o.B seems to need it. So let's talk about it. (Later on...days, weeks, who knows, maybe decades from now, depending on how much time this guy requires to get back to earth, he will probably say that he was just joking...well, we know it's going to happen...well, assumption that there is some intelligence there, he will do it at some point, but I'd be pretty sure he wasn't joking. He just made a discovery with his own small head.)

So, besides the masses thinking/knowing that the world is not flat, but indeed, round, how would you go about proving it to people like Bob?

On, here's what they say - "Start at One Point and Travel in the Same Direction for 25,000 Miles. If one person starts at one point and travels in the same direction for 25,000 miles, that person ends up at the same point. That proves the Earth is round and not flat. There are plenty of other ways to prove the roundness of our planet. The only reason ancient humans thought the Earth was flat was because their scope was limited to a very small area. Ancient Greeks knew the Earth was round 2,000 years ago by scientific measurements made in Egypt and Athens."

You can also just open your eyes and think (assuming you're able to) - When you're looking at ships moving further away, the masts are visible after the main body of the ship has disappeared beyond the horizon. If you go to higher ground, you can see farther.

But that's probably not enough for you either, so maybe see the videos below.

Carl Sagan's explanation

Reasons why we KNOW the earth is round