Luck of the irish 

This is an American phrase, not an Irish one. It’s an insult to Irish people that was coined during gold mining when a lot of Irish people arrived to make money suggesting they were stupid.

The idea was that if an Irish person could find gold then it was if to say, only by sheer luck, as opposed to brains, could these fools succeed.

-He got his promotion at work
-That’s the luck of the Irish for you

Luck of the irish by cupantae94 August 6, 2019

Irish Waterfall (Irish fish market, Luck of the Irish, Drunken Irishman) 

It's when a guy takes a full beer (preferably Guinness) and empties it in a womans vagina during intercourse. The man then proceeds to drink the alcohol from the opening as it flows out in similarity to a waterfall.

An Irishman is having sex with a lady, and decides to pour his beer right down her vagina in order for him to go drink, and lick it out while pleasuring his companion. This is then called an Irish Waterfall (Irish fish market, Luck of the Irish, Drunken Irishman).

Irish Waterfall (Irish fish market, Luck of the Irish, Drunken Irishman) by GregoryLarkinRonan March 18, 2010