Green’s Dictionary of Slang

(Irish) a wastrel, a rogue.

1966		H. Williams Speakers 43: I’m the king of the lachikoes, the king of the gypsies.
1970		C. Brown Down All the Days 175: They trust me, bejasus [...] They know I’m no fucking latchico or general foreman’s lick-arse.
1985		T. Murphy Conversations on a Homecoming (1986) 60: Watch that latchyco, Anne!
1989		R.E. Tangney Other Days Around Me 133: ‘What did you let him in for?’ roared the angry widow. ‘He’s the biggest latchico in town.’.