People act like the North Pole and the South Pole are exactly the same...
People act like the North Pole and the South Pole are exactly the same, but really, there’s a whole world of difference between them.
The humor in this joke relies in the two senses of the phrase "a whole world of difference". Normally, the phrase would mean "a lot of difference" in a figurative way, but in this case, the word difference is being punned with distance, and so the phrase is used to mean that there is a literal "large physical distance" (the entire planet) between them.
Now, difference and distance are not anything alike except for their starting and ending syllables, and no one would ever say "a whole world of distance", so this joke is absolutely awful.