The first three seasons were hilarious and I own them all, but they jumped the shark since then. Nothing but juvenile bathroom humor and rehashing of prior episodes these days.
EDIT:
SpongeBob SquarePants: What is air?
Patrick: Huh?
SpongeBob SquarePants: I just met this girl. She wears a hat full of... air.
Patrick: Do you mean she puts on airs?
SpongeBob SquarePants: I guess so.
Patrick: That's just fancy talk. If you wanna be fancy, hold your pinky up, like this. The higher you hold it, the fancier you are.
SpongeBob SquarePants: [Holds up pinky] How's this?
Patrick: Higher.
SpongeBob SquarePants: [holds his pinky up higher] Like this?
Patrick: Now that's fancy! They should call you SpongeBob FancyPants.
SpongeBob SquarePants: Hibernation? What's that?
Sandy Cheeks: It's when I sleep all winter.
SpongeBob SquarePants: Can I do that?
Sandy Cheeks: No, silly. It's a mammalian thing.
SpongeBob SquarePants: Sandy, you may not have noticed, but I is one-hundred-percent ma-male.
SpongeBob was funnier when he was heterosexual.