Definition of nyah-nyah in English:
nyah-nyah
(also nyah-nyah-nyah)
verb ˈnjɑːˌnjɑːˌnjɑːˈnjɑːˌnjaˈnja
with object To behave in a childishly supercilious or derisive manner towards someone; to taunt someone.
Origin
1980s; earliest use found in Adweek. Reduplication of nyah.