I can't believe nobody sent this to me yet: A Spongebob Squarepants version of Sir Mix-A-Lot's "Baby Got Back," as a Burger King commercial. Fabulously twisted.
Incidentally, the SpongeBob mash-ups on YouTube are all shades of hilarious. How about "The Final SpongeDown"?
Or Spongebob, "Walk It Out"
And, of course, unleashing the epic-ness of Motley Crue's "Home Sweet Home."