The Snape Kills Dumbledore fad began sometime in mid-July of 2005. Around then, the 6th Harry Potter book (Harry Potter and the Half-Blood Prince) was being released and it was mentioned that one of the main characters would not survive. When it was revealed it was Dumbledore, it quickly spread across the internet. A video then emerged of a person crashing Harry Potter release parties outside of several bookstores . The famed dialogue (near the end of the clip) was as follows:
Driver: "Hey! Snape kills Dumbledore!" Person waiting outside: NOOOOOOOOOO You Bitch! YOU BITCH!!"
The fad quickly exploded and showed no signs of stopping. The dialogue was used for various other sites. Interestingly, there were various varieties of the fad.
The page 606 fad involved altering the page where the spoiler was mentioned (page 606 of HBP). Various other fads would be shown in the form of the writing seen on page 606. The music of choice was "Tarzan Boy" from the "Gay Fuel" fad. The song is available on Volume 1 of the YTMND Soundtrack.
In 2007, as the release of the 7th Harry Potter book approached "Harry Potter and the Deathly Hallows", the spoilers returned. This time, they were leaked on the internet (and YTMND) a few days before the release on July 21st.