“Irish Alzheimer’s” is a jocular name for a supposed disease where an individual forgets everything except the grudges. The term was cited in the New York (NY) Post in 2000, when it was used by author Frank McCourt (1930-2009).
 
“Irish amnesia” is another term for the same condition, and a definition was published in the Urban Dictionary in 2008.
 
   
New York (NY) Post
A KICK IN THEIR ; ‘ASHES’ ; MCCOURTS FIRE BACK AT ACTOR HARRIS
By Steve Duleavy February 19, 2000 | 5:00am
“More than four decades of knowing [Richard Harris] — it’s a shock to find out he is suffering from Irish Alzheimer’s disease, where you forget everything except your grudges.”
(...)
The good name of Harris, who for 45 years has been a friend of Pulitzer Prize-winning author Frank McCourt and his family, went on trial in Midtown Manhattan after he blasted McCourt’s “Angela’s Ashes” as “shameless groaning and humorless moaning.”
 
Google Groups: rec.boats
Sheesh!!! Enough, already!!!
Russ Glindmeier
8/30/00
(...)
It’s hopeless, Steve.  Many here have suggested in a constructive manner that she let it go (whatever “it” is - I for one really don’t want to know) and just get on with things.  But instead, she insists on serving us the
same whine in different bottles, apparently thinking we’ll eventually develop a taste for it.  Irish Alzheimer’s perhaps.  Forgets everything except the grudges.
     
Jewish World Review
Sept. 26, 2000 / 25 Elul, 5760
Ann Coulter
I’d burn down my neighbor’s house
(...)
For those of you who don’t have Irish Alzheimer’s (we forget everything but our grudges), Rep. Chris Shays was one of only five Republicans to vote against the impeachment of a lying,
 
Google Groups: alt.support.mult-sclerosis
Can you trust drug companies?
.(JavaScript must be enabled to view this email address)
3/3/03
(...)
Tick, on this Alzheimer’s thing, I read somewhere there is a condition called Irish Alzheimer’s. You forget everything but the grudges.
 
Urban Dictionary
Irish Alzheimers
term in which one (typically, but not exclusively, an Irishman) doesn’t remember anything about his life except
 
his grudges and past quarrells.
usually the result of dwelling on negative past experiences instead of family triumphs.
(...)
by earth bound misfit June 13, 2007
 
Urban Dictionary
irish amnesia
forgive, but don’t forget.
person1:“She has irish amnesia.”
person2:“What’s that?”
person1:“She’ll always forgive you, but never forget what you’ve done.”
by Valerie_Grace July 15, 2008
   
New York (NY) Times
Paul Ryan’s Irish Amnesia
By Timothy Egan
MARCH 15, 2014
(...)
Irish Alzheimer’s, goes the joke, is to forget everything but the grudges — in the case of the great famine, for good reason. What Alexis de Tocqueville called “the terrifying exactitude of memory” is burned into Ireland’s soil. But more than forgetting, Paul Ryan never learned.
   
Mediaite
Trump’s New Grudge Against Megyn Kelly, Fox Good News for Rest of the Competition
by Joe Concha | 9:17 am, August 9th, 2015
(...)
There’s an old saying around suffering from Irish Amnesia…which consists of forgetting everything but the grudge.