I recently came across an interesting little comment from a certain Bob Fagan, who ran into Cassidy in an empty classroom in New College of California in 2005 or 2006. As Fagan says:
When I heard he was Professor of Irish Studies, I asked him if he had ever heard the theory that much Jamaican/reggae slang comes from Gaelic words that had entered their language centuries earlier, when Irish immigrants and indentured servants settled in Jamaica. Forgetting about his papers, he walked up to the blackboard and for the next ten minutes, wrote down every Jamaican slang term I threw at him, and figured out its Gaelic origins. It was obvious to me that this was a man in love with language, with teaching, as well as with learning. It was an unexpected, brief but truly delightful and memorable encounter.
I would love to have been a fly on the wall listening to Cassidy bullshitting that day. There is, of course, no evidence for Irish influence on Jamaican slang. A quick search on Google fails to turn up even one clear instance of an Irish or Gaelic slang term used in Jamaican patois. Even Montserrat, which has a much stronger claim to direct Irish connections, has almost no Irish influence on its speech patterns. (This source mentions one word which is found in Montserrat which is not found elsewhere and has a clear Irish origin, but generally finds the evidence of an Irish influence on the speech of Montserrat very underwhelming: http://www.phon.ucl.ac.uk/home/wells/brogue.htm)
I wonder what kind of rubbish Cassidy produced as he ‘figured out’ the Gaelic origins of these words for Bob Fagan that day. I’ll have a guess. No doubt, according to Cassidy, jah (in the real world, a shortened form of Jehovah) came from the Irish Dia (God), pronounced jeea. And I think he could well have suggested that irie, meaning good or excellent, comes from éirí, meaning rising or succeeding, though nobody has ever said “Tá sé éirí” in Irish.
Or perhaps (because Cassidy really didn’t know any Irish at all and I’m sure couldn’t have come up with even ludicrous fake Irish candidates without access to a dictionary) he just invented a load of random nonsense, plucking fake Irish words out of his arse to impress a total stranger. Because that’s what hateful ignorant narcissists like Cassidy do, invent a load of lying nonsense in a desperate, needy attempt to impress strangers, then leave the messes they create for other people to clear up.
cassidyslangscam 
I have had a message from someone (presumably they’re Jamaican) saying:
U need to re-research. One word example is the way we pronounce ‘face’.
No I don’t. I have looked for clear and unambiguous evidence by scholars and linguists that the Irish language or Irish dialects of English influenced Jamaican speech. There doesn’t seem to be any evidence. You claim (I presume this is what you’re saying) that the way you pronounce ‘face’ is in some way similar to the way many Irish dialects pronounce it. (But which ones? Belfast, Dublin, Cork, Donegal?) However, many Welsh people would pronounce it the same way. So would many people from the Newcastle area in the North-East of England. Did they also influence Jamaican slang? Or did they influence Jamaican slang instead of the Irish? I also have a friend from Nigeria and I think his pronunciation of ‘face’ would not be radically different from a West Indian pronunciation. Isn’t that a little more likely to be the origin of the phonetics of Jamaican dialect?
Also, anyone dealing with these issues would need to look at how English dialects have changed in other areas rather than Ireland. For example, many people assume that when some Irish dialects of English pronounce tea as tay or sea as say, this is because the Irish have changed these words. It’s a well-known fact among linguists that until the 18th century, tea and sea were pronounced tay and say in England as well. As the Irish were in the process of learning English from the English at the time, they learned it in that form, and then the English English changed to the current pronunciation, leaving an obsolete pronunciation in many parts of Ireland.
In other words, the fact that the word face sounds a little similar to some current dialects of Irish English is pretty flimsy as an argument and would need to be examined by a linguist with a knowledge of the relevant aspects of the history of English. However, if you come across any genuine academic articles or passages in books on Jamaican speech that confirm the Irish link, I would be interested to hear them.
I’ve got one for you
Jamaican slang for Tshirt = ganzi/ganzee
Irish for jersey = geansai (pronounced ganzi)
There’s many more instances like this out there
Seriously? This is your big revelation? I’ve already dealt with this:
“He says that the word gansey, meaning a jumper (or undershirt in the Caribbean) comes from Irish or Scottish Gaelic geansaí. But the word gansey almost certainly comes from Guernsey or Guernsey frock (just as jersey comes from the isle of Jersey) and geansaí is a relatively recent borrowing of gansey into Irish. I looked in the Corpas na Gaeilge, a huge seven million word database of Irish and there I found just one reference to the word geansaí, in a poem probably written in the early nineteenth or late eighteenth century. However, I was surprised to find that it isn’t a reference to the geansaí or gansey you wear, but to Guernsey itself: A bhfuil as seo go Geansaí /De fhíon, de bheoir is de bhrandaí (Of all that there is from here to Guernsey/Of wine, of beer and of brandy)”
In other words, gansey is an English dialect version of Guernsey and was used of a type of garment. Irish newspapers refer to shops selling gansey frocks as early as 1850 but there are plenty of references to such garments under the same name in non-Irish newspapers as well.. The first reference I can find to the use of the word geansaí to mean a garment in Irish is de Bhaldraithe’s dictionary in 1959, which is much later than the attested English examples of the word. As you say, in Ireland the word geansaí is often pronounced gansey or ganzi. Irish doesn’t have a z sound and if it weren’t a straight lifting of English it would be pronounced gyansee, not ganzi, of course. .
I heard Jamaicans in London refer to a “shebeen” as an illegal drinking establishment, i.e one without a licence. I have only ever heard that expression elsewhere in Ireland and they were astonished that I knew the word from Ireland, not from their “patois”.
As it says on Wikipedia: “The term has spread far from its origins in Ireland, to Canada, the United States, the United Kingdom, Zimbabwe, the English-speaking Caribbean, Namibia, Malawi, and South Africa.”
This suggests to me that shebeen is essentially an English word of Irish origin, like hubbub or brogue or puss. There has certainly never been any doubt among linguists about the Irish origin of the term shebeen, wherever it is found in the world.