Adj. Old fashioned. Possibly from antique(y) or antiquated. E.g."Oh no way! I'm not wearing those shoes, they're so antwacky." Merseyside/West Lancashire use
antwacky — adjective /æntwæki/ old fashioned or unstylish … Wiktionary
antwacky — adj British out of date, old fashioned. The term, used especially in northwest England, is probably a mock ignorant alteration of antique … Contemporary slang