Background and relevance Edit
During an episode of the show Six Feet Under, character Nate Fisher suddenly has a stroke, complaining about a "numb arm". The video in question is a brief clip of this scene.
The implied commentary is that the scene is intending to be dramatic, but comes across as unintentionally hilarious. The way that Nate devolves from saying "my arm's numb" to "numb arm" to "narm narm", as well as the seemingly exaggerated snort before he pratfalls backwards, has left many to find the scene humorous.
This scene has given birth to a trope called "Narm", referencing any scene in media which is unintentionally funny.
Lars uploaded this video in response to a lower-quality version of it from almost a decade beforehand, adding closed captions as well for those who needed or wanted them. TV Tropes links to Lars's video as of June 2019 on their article for Narm.