Since I've been on the internet since around 1996, I've seen a LOT of stupid things... probably the stupidest things I've seen in recent history was either the stanky legg or Soulja Boy's career as a whole. Short of that, I'd have to say those Fred videos that make pretty damn little sense in the comedic understanding. Why people attempt to milk a gimmick for years instead of trying to build on the success of such attention baffles me.
Short of performances, I'd say the next biggest stupid thing on the internet is people who sell food with images of religious figures on it... for a ridiculous amount of money. And people who outbid the first idiot to raise the amount to a monumentally stupid amount. As I recall, some dumb chick was selling her virginity on ebay to pay for her college tuition... of course, ebay shut down the auction after it garnered a good amount of publicity, but she had a high bid of $3.6 million from some brothel who took up her offer after ebay backed out of the auction. What ever happened to the stripper myth of dancing to Motley Crew songs to pay for school? Damn lazy kids with no rhythm.