For me it is This House Has People In It. There was a channel, I think it was Nexpo, that made a full hour video analysis on it and I'm still amazed by how much depth this has and how much effort went into it.
Saw this live on TV late in the night. Thought my television was broken then felt like I was going insane. At first I didn't realize it kept repeating, I wasn't fully paying attention, and then the video got so weird so fast. I forgot about it until the next morning and concluded it must have been a prank. Not too far off.
It's a parody of an 70s-80s sitcom intro such as full house or Brady bunch. It goes on for longer than you think, continually playing the theme song as more characters are introduced and slowly the whole thing devolves into surrealism.
I didn't know for years that this is an episode of a show called Infomercials which you can watch on Max. The first 5 or so episodes are spoofs of actual infomercials, but then it goes off the wall with episodes like this one. Highly recommended!
Whoa, neat! Apparently they sometimes show up just as blank spots on the Adult Swim TV guide, which I remember seeing in the past but had no idea what it meant.
They even have a Wikipedia page: https://en.wikipedia.org/wiki/Infomercials_(TV_specials)