Green’s Dictionary of Slang

(Irish) a gang of dissolute, rich young men who cut off the bottom few inches of their scabbards and prod or ‘pink’ with their exposed sword point those whom they encounter and with whom they can start an argument.

1778		Dublin Eve. Post 3 Nov. 3/3: Our active Chief Magistrate has declared war against pinkindindies, gamblers, sabbath breakers [etc].
1783		Hibernian Jrnl (Dublin) 22 Dec. 4/4: A general Meeting of the antient [...] Society of noct-ambulants, vulgarly called Pick-pockets, Gamblers, Bullies, Pinken-dindies, Foot-pads, and Draggled-drabs .
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Pinking-dindee. A sweater or mohawk. Irish.
1797		M. Leeson Memoirs (1995) I 69: At that time, Dublin was infested with a set of beings, who, however they might be deemed gentlemen by their birth, or connexions, yet, by their actions, deserved no other appellation than that of RUFFIANS. They were then called Pinking-dindies.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1847		(ref. to late 18C) J.E. Walsh Ireland Sixty Years Ago (1885) 17: Others were known by the soubriquet of Sweaters and Pinkindindies. It was their habit to cut off a small portion of the scabbards of the swords which every one then wore, and prick or ‘pink’ the persons with whom they quarrelled with the naked points.