It's a reference to I Wanna Be The Guy. The game has a lot of old school game references, and it's also brutally difficult. Just about anything and everything will kill you. Apples FALL UP to kill you (well, they're more like giant cherries...). You can get a game over AT THE END OF THE END CREDITS.
Anyway, here's why my quote is relevant: At one point in the game, you're in the Zelda 1 cave, and the old man with the sword, and he says his "dangerous to go alone" quote. If you jump on the sword (IWBTG is a side-scrolling platformer), it kills you like just about everything else in the game. The old man then says, "YOU JUMPED INTO A SWORD. YOU RETARD!"