noun: Trash, garbage, or filth.
Famously, in the 1970s BBC comedy "The Fall and Rise of Reginald Perrin," Reggie opened a doomed (he hoped) shop that sold old bits of trash and scrap recycled into completely useless items. He called it "The Grot Shop." (To Reg's horror, the shop was wildly successful, leading to a string of Grot Shops and, eventually, Grot Industries.)
Something that is "grotty" has a look of filth about it.
"Look at this wonderful planter I got at the Grot Shop."
"It looks like a grotty old shoe, to me."
A person who runs off at the mouth, and is completely full of shit.
Actually, the phrase is a combination of two Irish slang words scutter meaning diarhea, and gobshite, a person who doesn't know what they're talking about, but talks anyway.
A boreen is a small country lane, the kind that has grass growing up the middle of its single lane. Little more than a cartpath.
Boreens are often lined by close stone walls, so on the rare occasion one meets traffic comeing the other way, it can be all but impossible to pass without one motorist backing up for quite a distance.
We were out driving on the boreens of Roscommon when we came upon what I believe is the finest pub in the Republic.