Know the difference between the cool kids and the popular kids in high school? The popular kids care about seeming cool, but the cool kids don’t care if they’re popular. That’s what makes them cool. With that in mind, behold “21 Jump Street” (2012). It is a mediocre rip-off of a mediocre 1980s Fox network detective drama. But it doesn’t care. It sooooo doesn’t care. It drowns its mediocrity in profanity and wears its lack of originality like a crown of irony. Like a pair of hipster horn rims. Which is kind of cool, in a mediocre sort of way.