Americans have that general claim of being the best country in the world. The British do not like to make fun of the Americans as a nation. However, when it comes to internet trolling and online comment battles, certain internet trolls may call the American colonies, only to annoy them.
They also call the Atlantic Ocean the pond, but again, this is simply to annoy them and make a point. However, the British are not taught to actually call Americans this name in a serious manner. The use is just as a jest and should not be taken seriously by either party.
As a nation, the british do not call America the colonies. Usually, it is always a riposte to the claim of most of the Americans on the internet according to which America is the greatest country in the entire world. In general, the british are neither taught nor encouraged to call America the colonies.
However, a number of british people especially the internet trolls do love to annoy the Americans this way. It is quite similar to the way the Atlantic ocean is referred to as the pond. So most often, whatever similar said is usually in the form of satire and does not have to be taken seriously.