IN THE WORLD
Used as an abbreviation for saying "the best theme park/ride/roller coaster/anything really in the world", although the the saying must be emphasised or shouted in a monotone fashion, or it isn't likely to make sense to anyone.
Often whoever is saying "IN THE WORLD" won't actually mean that it's necessarily their favourite *whatever* in the world, just that it's really rather good and could be considered one of the best.
The origins of this particular meme are ostensibly rooted back to Europa Park, where a group of TS members found amusement in pointing at all the less-than-adequate elements of the park (e.g. Euro Mir's queue line, Bench and the Adventureland area) and shouting "IN THE WORLD" in response to everyone saying that EP is the best theme park in the world. This joke seems to have turned of recent years though, back to meaning that something genuinely is good.