Many comic book super-hero fans have long known that Hal (Green Lantern) Jordan is the KING of head trauma -- and we can probably all thank Sleestak for keeping that knowledge well-documented and publicly available.
HOWEVER, I put it to everyone that Hal is NOT necessarily solely responsible for being such a klutz when it comes to his cranium. There's evidence that he's merely following in the footsteps of some higher-ups. And if these higher-ups were ever to give Hal tips on how to avoid getting whacked in the head, I think it's safe to state that he wouldn't pay any more attention to them than he usually does -- which is probably a good thing:
I just hope that isn't Ganthet!