A time in the 1900s the 1990s was a fun jazzy time but was less 70s and more 21st century.

I couldn’t care less (but one must keep up appearances, right?)

English word in use in Ireland with the meaning of

(1) Completely wonderful, great, fantastic, etc. or
(2) Lost the head.

Typically used in schools. When a teacher or supervisor's not around and the student aren't doing what they're supposed to (i.e. Using their device, fighting, etc), a student that first notices a teacher is coming to their classroom yells to the class, "NINETY!". Which is a code word meaning a teacher is coming. The students can then quickly get back to what they're supposed to do.