youtube poop is basically screwing with a video until it makes absolutely no sense. here are some people that make ytp:
http://www.youtube.com/MrTennek
http://www.youtube.com/SeductiveBaz
http://www.youtube.com/CorruptionSound
http://www.youtube.com/madanonymous
http://www.youtube.com/Metzgorrre
http://www.youtube.com/TheDykeVanDickShow
there are a lot more poopers then that, though. for a list of a lot of them, a lot more information about ytp check out http://www.youchew.net/wiki