Do you know Japanese popular phrase "Ima desho!: Do it now!" ?

The phrase “Ima desho!,” or “Now!,” first became popular online last year, but it has taken on a life of its own after Toshin High School literature teacher Osamu Hayashi spat it out at the end of a Toyota commercial.

But this pen case says "Ima jyanai desho! : Not now!"

If you can understand why this is funny, get it now　щ（ﾟдﾟщ）