Green’s Dictionary of Slang

1. unexciting, unexceptional, uneventful.

1971		Current Sl. VI 1: Basic, adj. Fundamental, according to the norm.
1975		G. Underwood ‘Razorback Sl.’ in AS L:1/2 56: It was your basic date; he took me to a movie.
1981		Eble Campus Sl. Fall 1: basic – free of complications: Her actions were so basic.
1990		Eble Campus Sl. Nov.

2. (US) immature, unsophisticated.

2014		C. Eble (ed.) UNC-CH Campus Sl. Spring 2014 2: BASIC — unintelligent, immature: ‘That basic girl is trying to get attention by wearing that short dress.’.
2016		C. Eble (ed.) UNC-CH Campus Sl. Fall 1: BASIC — unoriginal, uninteresting, following popular trends: ‘We went on a few dates, but she was so basic. She didn’t even have an opinion on this election’.