The official name for the invasion that took place on pages 22, 23, and 24 of part Part 15. It managed to (albeit unintentionally) completely stop the ongoing wank that had been taking place previously.
The Butt Invasion was planned within a page and a half's time, but it still managed to come out fantastic. After the original discovery of a utterly disturbing picture of a butt, a group of anons gathered in secret to discuss in length the hair and pimples they could see as the picture was enlarged. They decided: The meme must see this!
At first they tried proxies, so as not to get banned. Unfortunately, it didn't work. Then one of them had the brilliant idea to create a new account! Anon took the lead and made buttanons, as another anon got to work on userpics. The anon who made the account posted another anon's poem and the South Park music video, "What What in the Butt", added appropriate keywords, and made related tags to set up the account fully.
The invasion took places over three pages. Originally it was slated to last only two, but multiple anons urged it forwards. They continued, past the wee hours of morning they had already stayed up to, until daylight broke over the hills. They ended together in one short thread.