The full form of YTP is YouTube Poop

YTP stands for “YouTube Poop”. This does not mean videos of fecal matter on YouTube, but instead a genre of humorous videos. Creators of these videos, called “Poopers”, would take videos from popular television, movie, or video games and mash them together using video editing software. YouTube Poop videos are well-known for their bizarre humor, with the videos rarely having a coherent plot and designed to throw out as many jokes and gags, to the expensive of the source material, as possible.

Origin of YTP
YouTube Poop began on December 22, 2004 when an internet user using the name “SuperYoshi” made a short video using Windows Movie Maker. The video took an episode from the old cartoon The Adventures of Super Mario Bros. 3 and with the software SuperYoshi edited the footage in a random manner. When posted online, the video got positive reception encouraging SuperYoshi to make more videos like it. As the videos became more popular they shifted from being completely bizarre and tried to focus on some narrative structure, even if said narrative didn’t make much sense. By the 2010s, YouTube Poops suffered a massive decline in popularity due in part to other more professional humor videos overtaking them and YouTube cracking down on any copyright infringements, which many YouTube Poop videos had.

Conversation Examples
Online Discussion

User 1: “Whatever happened to YTP?”
User 2: “YTP?”
User 1: “YouTube Poop.”
User 3: “You don’t remember YouTube Poop?”
User 2: “No?”
User 3: “They were these random videos on YouTube. I loved the Mario ones.”
User 1: “I think YTP got in trouble because of copyright looking it up. What a shame.”