It's not only in a ton of cartoons (spongebob, well...come to think of it...nearly anything on nickelodeon), it's in a ton of adult shows, radio shows, plays, books, etc. In most of them, it's used humorously so it goes right over our radar...but "out of the mouths of babes"...they get the intent, but not the humor...so it sticks.
My son's favorite way of showing frustration until preschool was to say "stupid 'ting!" to whatever (not whoever) was giving him problems. His preschool drummed that out of him (they weren't allowed to say the word at all), and he picked up kicking the thing instead. Sigh.
To this day he gets horrifically upset if ANYONE uses the word stupid...where as before, it was fairly inconsequential.
Double edged swords and all of that.
R