What's the worst/weirdest thing you've ever seen on the internet? I'll go first. (Depending on the comments, possibly [NSFW] or [NSFL])

This is probably really tame, compared to others, but I was just fucked up for days after seeing Jeff The Killer (just image search the thing, I don't want to dredge the photo up). It was the first creepypasta that actually scared me, all because of the photo. The weirdest, on other hands, is El Goonish Shive.

EDIT: After reading the comments, my reaction to the orange letter is now permanently set to this.