"Doomsday" revealed to us in a funeral scene that "Jimmy Olsen" who we've been watching since the start of Season 8 is actually not the Jimmy Olsen we all know from the comics - but is rather his older brother, Henry James Olsen.
Because there was no build-up (a bow-tied kid appearing at the wedding in "Bride" may have helped) people seemed kind of blindsided and in many cases, duped.
33% of the folks who voted picked that as the Biggest What The Heck?!? Moment for Season 8 of Smallville.
Lana getting a suit to make her "Super Lana" in "Power" came in second place (1110 votes), and Davis Bloome killing Jimmy in "Doomsday" came in third (804).