For my own reference, as much as anything else.  I’m only listing things I’ve heard people say frequently that might not be obvious to a non-national:

Baltic: cold.  Note to people from the north of England: this does not mean cold.

Blow-in: someone from outside the area.  People often refer to themselves in a self-deprecating manner as a blow-in even though they’ve lived in a place for 30 years or more.  I think it’s mainly used to illustrate that you’ll never be fully accepted as a local  somewhere, but in a nice, slightly arch, kind of way to say it doesn’t really matter.  Compare with: the Welsh burning-out English-owned holiday homes.

C’mere: excuse me, listen, that sort of thing.  Not “come here”.

Feck: three common uses… expletive, verb to throw, verb to steal.  Not sure if can be combined into something like “Feck!  He’s fecked my phone and fecked it over the fence” – it sounds slightly contrived.

Gas: hilarious.  “It was gas”, “he’s gas”, etc.

Grand: great / good / whatever.  “It’ll be grand” is the verbal equivalent of a pat on the head and being told not to worry.  Even though you should.

Hot press: airing cupboard.  Press on its own can be just a cupboard.

Lads: refers to a group of people, whatever the gender make-up of it.

Long finger, on the: delaying something.  Q: “Shall we drill a hole to ventilate the cloakroom and prevent extreme damp?” A:  “No, that’s a messy job – best put it on the long finger”.

NCT: Irish equivalent of the British MOT test for vehicles.  Presumably this ensures that for at least a very brief period people have cars with both headlights working.

PRSI: Social security.  The British equivalent would be National Insurance, and in Ireland a person is identified by a PPS number in this system.

Stocious: very drunk.

Strand: beach.  Same as German language and a bunch of others (see: https://en.wiktionary.org/wiki/strand#Etymology_1)

Streelish: untidy / unkempt.

Sure: appears at the start of some sentences to lend an air of confidence in the veracity of what follows.  Not to be trusted.

Ye: you (plural).  A useful distinction in the language that would otherwise need the vastly more complicated “you all”.

Yer man / yer one: Not actually anything to do with you, despite the possessive hint at the start.  Used to refer to someone else in a non-specific way.  Massively confusing at first.