Google Seppuku is a "game" invented by webcomic artist Ghastly as a punishment for his children. He later posted a description of the game in his comic, to settle a bar bet over whether any of his readers were stupid enough to try it. Much to his surprise, the meme spread quickly, mostly among the incurably insane (who make up about 90% of the regulars on teh internets).
The game is played by entering random combinations of Japanese characters into the Google Image Search tool and then scanning through the results until you find an image that makes you want to kill yourself. Given the perverse nature of the Japanese, this rarely takes long.