Q:

Difference between 'prank' and 'hoax'

The two words have a pretty similar meaning of 'malicious trick' or 'deception scheme'. My impression is that 'hoax' is more formal on one hand and more wicked, less playful on the other hand.
Surely there are many contexts in which they are not likely to be interchangeable. I'd like to hear what are the native-speakers' impressions on the subtle differences between the two terms
In particular, what would you choose in:

"UFO stories are probably the greatest/biggest hoax ever played on mankind"

.
Do you use the verb 'to play' with 'hoax'? What are the most usual alternatives, is 'perpetrate' too formal?

A:

A hoax is something that encapsulates the idea of deception, typically on a large group of people. Often there is no element of humour in a hoax, instead the principle aim is to confuse or scare. A hoax normally has long term consequences and mysteries that are never resolved. This has created many modern day 'legends' e.g. Loch Ness Monster, Bigfoot, Roswell, etc.
(dictionary.com)

noun

something intended to deceive or defraud:

Example: The Piltdown man was a scientific hoax.

A prank on the other hand describes a (often lighthearted) trick played on someone you know, or on a small group of people. Typically involving some kind of physical humour intended to temporarily confuse or scare someone. However, a prank can also take on a darker sense of humour too. A good example of the spectrum of 'darkness' would be convincing a friend that their dog has died vs pretending to be a statue and then jumping out at people.
(dictionary.com)

noun

a trick of an amusing, playful, or sometimes malicious nature.

As for your last questions, you can definitely play a hoax on someone. Hoax itself is also a verb so in some circumstances it may just be simpler to use it that way.
It also makes sense to say that UFO stories are a hoax. Although a small pedantic point: the concept of UFO stories is not a hoax in my opinion as they cannot be pinned down to a single event and are by definition 'unindentified flying objects'. You could certainly say something more specific like "crop circles were the biggest hoax ever played on extraterrestrial believers".

