Green’s Dictionary of Slang

nitty adj.

also knitty
[lit. suffering from SE nits, lice]

a general epithet of abuse.

[UK]Nashe Pierce Pennilesse 20: A malecontent Cutpursse [...] cannot his stabbing dagger, or his nittie loue-locke, keepe him out of the Legend of fanatasticall cockcombs.
[UK]Jonson Poetaster n.p.: I’le know the poore, egregious, nitty Rascall.
[UK]Massinger Virgin-Martyr III iii: Sure thy father was some botcher, and thy hungry tongue bit off these shreds of complaints, to patch up the elbows of thy nitty eloquence.
[UK]J. Taylor Crabtree Lectures 50: Thou lousie nitty Tayler.
[UK]New Brawle 7: [T]hou Villaine, thou nitty Breech’d Knave.
[UK]Mercurius Fumigosus 34 17–24 Jan. 268: A one-ey’d Tool-man, called a Taylor, being sore troubled with a Hunting Wife, that would nether let him lick his Thimble, nor winde up his Bottom in quiet, but would follow him open-mouth’d, calling him drunken Roague, Nitty-breech’d Roague.
[UK]Greene & Lodge Lady Alimony IV ii: Doth your Mistress take us, you nitty-napty Rascal, for her Bordella’s Blouses?
[UK]T. Porter The French conjurer 15: A Pox take that nitty confounded French man.
[UK]N. Ward London Spy VII 154: Hold your Tongues you Knitty radish-mongers.
[UK]Bridges Burlesque Homer (3rd edn) 71: You nitty, lousy, hump-back’d toad.

In compounds

nitty-breech (n.)

a general insult suggesting a lower-status target, actual nits may not be present.

[UK]Dekker Penny-vvis[e] pound foolish n.p.: Away you lowzie Slaue, cried the Pandar, my Mistresse a companion for such a Nitty-breech as thou art, to talke to her!
[UK]A sea-cabbin dialogue 10: [C]all me Foole, Nitty-breech, Ninny-hammer, Cocks-cumbe, or any thing what thou wilt.