However, I fear it is a "local" joke that my international friends and followers may not get it.
So before I tell the joke let me give you a bit of a an Irish "lingo" lessson.
Here in Ireland we use a word to describe fun - craic.
So describing a night out you might say "it was good craic". You might also say about something like "ah sure isn't it a bit of craic"
It's a commonly used word here in Ireland and everyone knows what it means.
Okay so the next bit is important for the joke!
It also can be used as a type of greeting/salutation
e.g. "What's the craic?" Or "How's the craic" Or "Any craic"
A bit like "What's up" I guess.....