O
- 20 on the blue ladCork
- O shur hayTipperary
- O the green and redMayo
- OatsLimerick
- OblockKerry
- OckyTipperary
- Ocky JimmyDonegal
- OddCork
- Odd sortTipperary
- OddballDublin
- OddsSligo
- OddsWaterford
- OdejushCavan
- OdiousCavan
- Odious - pronounced ojousLongford
- OdjiousCavan
- Of my lifeLimerick
- Of the highest orderTipperary
- Of your faceLongford
- Off da clockSligo
- Off for a slash heyLouth
- Off his nutKilkenny
- Off his rockerCork
- Off his titsGalway
- Off in a hackKilkenny
- Off me boxSligo
- Off me faceKilkenny
- Off me head!Sligo
- Off my gameCork
- Off my nopperClare
- Off the fasMayo
- Off the neuckMayo
- Off the rackArmagh
- Off to chattanoogaMayo
- Off your chompDublin
- Off your head!Dublin
- OffieCork
- OffieDublin
- OffyaLimerick
- OgeousMonaghan
- Oh be the lord harryWexford
- Oh de cross a Jaysus!Offaly
- Oh God yeah!Tipperary
- Oh laad!Cavan
- Oh llaaaddd!Cavan
- Oh man dearCavan
- Oh my cockDublin
- Oh nora batty!Dublin
- Oh the holy handsOffaly
- Oh vu!Cork
- Oh ya dingbat!Kilkenny
- Oh yur toughKerry
- OhjussCavan
- OinseachKildare
- OinseachLaois
- OinseachMayo
- Ol ladeCork
- Olagonin'Tipperary
- Old beanTipperary
- Old billDublin
- Oldtimer's diseaseKilkenny
- OlyanWexford
- OlyawnCarlow
- OmCork
- Omg showWestmeath
- OmprasLeitrim
- On a 50/50Cork
- On a hornDublin
- On a wild oneGalway
- On d'townLaois
- On da hopCork
- On da tearDonegal
- On de ballKerry
- On de ballWaterford
- On de dossWaterford
- On de mopCavan
- On de prowlCork
- On me solmn oathMayo
- On me toblerDublin
- On the ballWaterford
- On the ballWaterford
- On the batterCavan
- On the batterWaterford
- On the blobMayo
- On the brownGalway
- On the dagTipperary
- On the dossCork
- On the duckWaterford
- On the hopCork
- On the jobCork
- On the kildare sideDublin
- On the langCork
- On the langKerry
- On the lashDublin
- On the lashGalway
- On the lashTipperary
- On the lashWaterford
- On the nestDublin
- On the picnic danger listMayo
- On the pig's backRoscommon
- On the ragWaterford
- On the ragsCork
- On the rantanWaterford
- On the razzWexford
- On the RicoCork
- On the road!Sligo
- On the sauceCork
- On the troopSligo
- On the wagonDublin
- On yer toddCork
- On your bicycleMeath
- On your ToblerDublin
- On-realWaterford
- OndaWexford
- One & oneDublin
- One 'n da barrow an' one in da mixerDonegal
- One and oneDublin
- One anotherDublin
- One cheek sneakLimerick
- One hundredacementMonaghan
- One of the damndestRoscommon
- Oneow / 0neowsWicklow
- OneyDublin
- Onion bagKilkenny
- OnlyDublin
- Only a pupLouth
- Only a slip of a thingWaterford
- Only coddinSligo
- Only coddin'Roscommon
- Only touchin' da road in spotsDonegal
- OoftWestmeath
- OoommmgggSligo
- Oops-a-daisyDublin
- OpDublin
- Open a can o' wormsDonegal
- Open sandwichAntrim
- Or whateverWexford
- Orange cosLimerick
- OrdinaryAntrim
- OssifiedCork
- OssifiedDublin
- OssifiedGalway
- OssifiedKildare
- OssifiedLongford
- OssifiedMayo
- OssifiedSligo
- OssifiedTipperary
- Ou'witchya!Waterford
- Oul boy / lassLongford
- Oul dollCork
- Oul fellaCork
- Oul fellaWaterford
- Oul pairCork
- Oul stockCork
- OurCavan
- Our 1Monaghan
- Our bayhTyrone
- Our bladeArmagh
- Our bladeTyrone
- Our boyMonaghan
- Our dollMonaghan
- Our manTipperary
- OutCork
- Out an out bastardTipperary
- Out in da sticksDonegal
- Out like a lightTipperary
- Out of his treeDublin
- Out of me barnetDublin
- Out of me binDublin
- Out the doorCork
- OutaCork
- Outa itSligo
- Outa my wheelie binWexford
- OutsiderGalway
- Outta me face!Dublin
- Outta the sceachsWicklow
- Outta yerr nuggetCarlow
- OuvitKildare
- OvaCavan
- Over dere lahCork
- Over nite skankGalway
- Over the bar is the place for it ladsKerry
- Over the hillTipperary
- Over the moonCarlow
- Over yonderDonegal
- Over-rightWaterford
- Overheating like a randy badgerKerry
- OverrightKilkenny
- Ow'l yokeGalway
- Owl flowerTipperary
- Owl forka bushesTipperary
- Owl handTipperary
- Owl hatchin hinTipperary
- Owld wanWaterford
- OxoDublin
- OxterAll Ireland
- OxterDonegal
- OxtersKilkenny