The humor. The increasing homosexual actions/thoughts that Spongebob has such in 20,000 Patties Under the Sea where he says this:
SPONGEBOB: "Good bye Squidward! Good bye Mr.Krabs! Good bye Squidward."
PATRICK: "Spongebob?"
SPONGEBOB: "Yeah Patrick?"
PATRICK: "You said goodbye to Squidward twice."
SPONGEBOB: "I know, I like Squidward."
To the straight out suggestive matterial when the camera zooms on the hotdogs those nerds/geeks/spazes are having at Super Weenie Hut Juniors from the episode No Weenies Allowed.
And then there is a plain humor that children get like Patrick being stupid such in I Had An Accident.