Green’s Dictionary of Slang

above oneself, cheeky, ‘clever’.

1806		Jamieson Popular Ballads I 297: Tam Tod was [...] Slee, snackie, and wilie, and quirkie .
1860		R. Nicholson Rogue’s Progress (1966) 104: Whenever the little bruiser gets snacky [...] I am obliged to set him right [...] by some jocose observations which drive him mad.