recherchez un mot, comme dirty sanchez :
 
1.
A particularly unpleasant hangover.
"Last night was great, but I have the worst case of the irish flu today."
de Melissa 10 juillet 2004
 
2.
A hangover, usually involving whiskey; may be mild or severe
"I’ve still got a touch of the Irish flu."

"The Irish flu?"

"Also known as a hangover."

(from "A Nose for Murder" by Lee Charles Kelley
de Lee Charles Kelley 6 avril 2005
 
3.
The ailment one suffers on March 18th after properlyly celebrating St. Patrick's Day. Anyone of Irish descent may also use the term to denote a hangover on any day of the year.
Seamus: Ugh, I was out drinking Guinness until the wee hours. I think I'll call in with the Irish Flu today.
de robbie vienna 17 mars 2009