YouTube Poop is a popular internet meme that involves editing or mashing up of videogame cutscenes, TV episodes, movies, advertisements, or anything that is a video into a humorous internet video. In some cases, the poop (YouTube Poop video) can involve turning a simple videogame cutscene or ad into an elaborate story. It reached peak popularity (so far) in 2011, but is still popular and moving on the rise.
The opinion of YouTube Poop is mixed - lots of people like it, lots of people hate it, and lots of people either don't care or don't know about it. It has become very popular and has either absorbed or created new memes, and those who like the new memes probably like YTP in some way. However, many people hate it and call it stupid or gay. They either have only seen the most amateur poops, or they're just very closed-minded. Many of the rest don't know what it is, and when they see a YouTube Poop in the related videos section, they'll wonder what they just watched and end up confused (ironically, that was the original purpose of YTP, but not anymore). Some will call it "the weird side of YouTube" no matter how good the YTP really is.
In the early days (but a year or two after it was invented, not at the beginning) of YouTube Poop, people would place an introduction at the beginning of the video, just to make viewers identify it as a YTP. The first one came from the Hotel Mario cutscenes. The quotes "Be careful! When you pinch Wendy's pennies, they pinch back" and "Remember, where there's smoke were edited, and the resulting intro stated: "Where there's smoke, they pinch back!" (Note that Hotel Mario was before Mario started speaking in an Italian accent). Eventually this was edited more so that a logo was added, the voice was changed, and sometimes even a nuclear explosion would appear in the background.
Some time later, a new intro was created: "YouTube Poop is where the Poop is!", following by Luigi (from the SMW cartoon, long before the Italian accents) wheezing ryhtmically to a jingle. This is the second-most popular intro. Both intros have been parodied, where "smoke" and "pinch back" may be replaced by something else, and the Mama Luigi clip might be removed, and "poop" might be replaced with something else. Other intros have been created and used, but none are nearly as common as the aforementioned two.
Some YTPs (including most Billy Mays ones) don't have an intro at all.